• Communications of Mathematical Education
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• v.29 no.3
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• pp.533-551
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• 2015

Problem posing in school mathematics is generally regarded to make a new problem from contexts, information, and experiences relevant to realistic or mathematical situations. Also, it is to reconstruct a similar or more complicated new problem based on an original problem. The former is called as problem generation and the latter is as problem reformulation. The purpose of this study was to explore the co-relation between problem generation and problem reformulation, and the educational effectiveness of each problem posing. For this purpose, on the subject of 33 pre-service secondary school teachers, this study developed two types of problem posing activities. The one was executed as the procedures of [problem generation${\rightarrow}$solving a self-generated problem${\rightarrow}$reformulation of the problem], and the other was done as the procedures of [problem generation${\rightarrow}$solving the most often generated problem${\rightarrow}$reformulation of the problem]. The intent of the former activity was to lead students' maintaining the ability to deal with the problem generation and reformulation for themselves. Furthermore, through the latter one, they were led to have peers' thinking patterns and typical tendency on problem generation and reformulation according to the instructor(the researcher)'s guidance. After these activities, the subject(33 pre-service teachers) was responded in the survey. The information on the survey is consisted of mathematical difficulties and interests, cognitive and affective domains, merits and demerits, and application to the instruction and assessment situations in math class. According to the results of this study, problem generation would be geared to understand mathematical concepts and also problem reformulation would enhance problem solving ability. And it is shown that accomplishing the second activity of problem posing be more efficient than doing the first activity in math class.

• Communications of Mathematical Education
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• v.28 no.2
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• pp.255-279
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• 2014

This study is to investigate the change of intelligent and affective domains through the student self-evaluation to identify causes of wrong answers. Through this evaluation, students could have opportunities to solve the given mathematical problems basically and to reflect their problem-solving process, and further to recognize which mathematical content(concepts or expressions, symbols, etc.) led them to solve the problems incorrectly or wrong. Through this process, they would correct their wrong process and answers and to reinforce the prerequisite knowledges relevant to the problems, and furthermore, to enhance problem-solving abilities. To accomplish this, this study was executed as a case study on the subject of four tenth graders. The subject consisted of two boys and two girls. In this study, three essay types of mathematical problems in tenth grade level were chosen from several domestic tests in Korea. Based on the original three essay type of problems, three types of similar problems, namely equivalent problem, similar problem, and isomorphic problems were reconstructed, respectively by the researchers. The subjects were guided to solve the original three problems, and they corrected their wrong parts of the first problem of the three problems. They solved an equivalent problem of the first problem and executed self evaluation and also corrected wrong parts. Next, they dealt with a similar problem of the first problem and executed self evaluation and also corrected wrong parts. Next, while dealing with an isomorphic problem of the first problem, the subjects did the same things. Thus, for the second and third original problems, the study was implemented in the same way. To explore their intelligent and affective domains through student self-evaluation in-depth, the subjects were interviewed formally before and after conducting the experiment and interviewed informally two times, and the recordings were audio-typed.

• The Korean Journal of Applied Statistics
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• v.31 no.1
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• pp.77-96
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• 2018

A reverse mortgage provides a pension until the death for the insured or last survivor. Long-term risk management is important to estimate the contractual period of a reverse mortgage. It is also necessary to study prediction methods of mortality rates that appropriately reflect the improvement trend of the mortality rate since the extension of the life expectancy, which is the main cause of aging, can have a serious impact on the pension financial soundness. In this study, the Lee-Carter (LC) model reflects the improvement in mortality rates; in addition, multiple life model are also applied to a reverse mortgage. The mortality prediction method by the traditional LC model has shown a dramatic improvement in the mortality rate; therefore, this study suggests mortality projection based on the projection of the skewness for the mortality that has been applied to appropriately reflect the improvement trend of the mortality rate. This paper calculates monthly payments using future mortality rates based on the projection of the skewness of the mortality. As a result, the mortality rates based on this method less reflect the mortality improvement effect than the mortality rates based on a traditional LC model and a larger pension amount is calculated. In conclusion, this method is useful to forecast future mortality trend results in a significant reduction of longevity risk. It can also be used as a risk management method to pay appropriate monthly payments and prevent insufficient payment due to overpayment by the issuing institution and the guarantee institution of the reverse mortgage.

• Communications of Mathematical Education
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• v.25 no.1
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• pp.261-288
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• 2011

We examined the effects of pair assistant collaborative learning on academic achievement of the 2nd year middle school students in the three subjects such as the Probability, Properties of Figures and Similarities of Figures. In order to carry out this study, we selected 2 classes of 2nd year students in a girls middle school in the Fall semester of 2009 and set up the experiment group and comparison group by the result of academic achievement tests given in the end of the Spring semester of 2009. Pair assistant collaborative learning was adopted for students in problem solving 2 or 3 times per a week in the experiment group and each academic achievement was given at the end of each subject in both groups. Also, we had a final survey to find out students' attitude to this collaborative learning. The achievement and survey were analysed by statistical methods. We conclude that our pair assistant collaborative learning was effective in Probability and Similarities of Figures Units. According to the result of survey, this collaborative learning brought about an opportunity to promote students' community spirit through reflecting each one's role in the group.

• Journal of Gifted/Talented Education
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• v.16 no.2
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• pp.167-191
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• 2006

The purpose of this study was to explore logical thinking abilities and metacognitive characteristics by student's giftedness and grade level. Furthermore, this study sought to present the practical basis for the promotion of students' abilities in self-driven learning as well as cognition. Average-ability students(n=199), economically disadvantage gifted students(n=133), and gifted students(n=111), who were sampled by two-step sampling procedures, responded the logical thinking ability test(Cho et al, 2006) and the questionnaire asking self-perception for 'metacognitive knowledge' and 'metacognitive control' abilities(Cho & Han, 2004). As the results, average-ability students showed less logical thinking abilities(in language, mathematics, and space) than gifted students. The logical thinking abilities had affected by giftedness, grade level and these interaction. And gifted students showed higher metacognitive control abilities in planning, monitoring, priority, and strategies of learning than average-ability students. However, there were no significant differences in metacognitive knowledge and metacognitive control abilities between economically disadvantaged gifted students and gifted students.

• Journal of the Korean earth science society
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• v.34 no.6
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• pp.492-506
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• 2013

The historical accounts and materials about the eruption of Mt. Baekdusan as observed by the geological survey is now showing some signs of waking from a long slumber. As a response of the volcanic eruption of Mt. Baekdusan, water release may occur from the stored water in Lake Cheonjii caldera. The volcanic flood is crucial in that it has huge potential energy that can destruct all kinds of man-made structures and that its velocity can reach up to 100 km $hr^{-1}$ to cover hundreds of kilometers of downstream of Lake Cheonji. The ultimate goal of the study is to estimate the level of damage caused by the volcanic flood of Lake Cheon-Ji caldera. As a preliminary study a scenario-based numerical analysis is performed to build hydrographs as a function of time. The analysis is performed for each scenario (breach, magma uplift, combination of uplift and breach, formation of precipitation etc.) and the parameters to require a model structure is chosen on the basis of the historic records of other volcanos. This study only considers the amount of water at the rim site as a function of time for the estimation whereas the downstream routing process is not considered in this study.

• Journal of Biomedical Engineering Research
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• v.19 no.6
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• pp.551-562
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• 1998

Amultiresolution filtering algorithm based on the physical SPECT lesion detachability provides and optimal solution for SPECT reconstruction problem. Related to the previous study, we estimated the SPECT lesion detection capability by m minimum detectable lesion sizes (MDLSs), and generated m reconstruction filters which are designed to maximize the smoothing effect at a fixed MDLS-dependent resolution level $\frac{MDLS}{4\sqrt{2In2}}$. The proposed multiresolution filtering algorithm used a coarse-to-fine approach for the m-level resolution filter images obtained from these m filters for a given projection image. First, the local homogeneity is determined for every pixel of the filter images, by comparing the local variance value computed in a window centered at the pixel and the mode determined from the distribution of the local variances. Based on the local homogeneity, the pixels declared as homogeneous are chosen from the filter image of the lowest resolution, and for the other pixels the same process is repeated for the higher resolution filter images. For the non-homogeneous pixels after this pixels after this repetition process ends, the pixel values of the highest resolution filter image are substituted. From the results of the simulated experiments, the proposed multiresolution filtering algorithm showed a strong smoothing effect in the homogeneous regions and a significant resolution improvement near the edge regions of the projection images, and so produced good adaptability effects in the reconstructed images.

• Korean Journal of Food Science and Technology
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• v.39 no.3
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• pp.266-271
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• 2007

The pH, acidity, color, reducing sugar, total sugar, alcohol, and organoletic characteristics of Takju containing puffed rice powder (0, 25, 50 and 75%) were investigated during fermentation for 10 days. After drastic decrease at Day 1, the pH increased gradually until Day 5 and then tended to decrease after Day 6. A lower concentration of puffed rice powder resulted in a greater pH reduction (p<0.05). Acidity increased quickly with days, especially for the 0% after Day 6 (p<0.05). After a sudden rise at Day 1, the Hunter ‘L’ value tended to decrease with days of fermentation. At the same day, the 75% showed the lowest Hunter ‘L’ value, however, it had the highest Hunter ‘a’ value except on Days 0, 3 and 10 (p<0.05). After a rapid reduction in reducing sugar on Day 3, no differences were observed in the samples (p<0.05). The 75% tended to be higher in reducing sugar. Total sugar decreased rapidly at Day 2, and then either remained unchanged or decreased after Day 3. With the exception of Day 4, the 75% had higher amounts of total sugar than the others at the same day (p<0.05). The Highest alcohol contents [13.0-16.4% (v/v)] occurred on Day 6. Higher alcohol concentrations were observed with higher puffed rice powder (p<0.05). In the sensory evaluation, no differences were detected between the 0% and those with puffed rice powder added (p<0.05).

• Journal of the Korea Institute of Information and Communication Engineering
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• v.20 no.12
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• pp.2243-2251
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• 2016

In this paper, we propose a theoretical model for characterization and upper bounds of [1,2]-domination set of network which has tree structure. In detail, we propose a theoretic model for upper bounds on [1,2]-domination set of a tree network which has some typical constrains. To that purpose, we introduce a graph theory to model and analyze the characteristics of tree structure networks. We assume a node subset D of a graph G=(V,E). We define that D is a [1,2]-dominant set if for any node v in set V which is not an element of a set D is adjacent to a node or two nodes of an element in a set D (that is, $1{\leq}{\mid}N({\upsilon}){\bigcap}D{\mid}{\leq}2$ for every node $v{\in}V-D$). The minimum cardinality of a [1,2]-dominating set of G, which is denoted by ${\gamma}_{[1,2]}(G)$, is called the [1,2]-domination number of G. In this paper, we show new upper bounds and characteristics about the [1,2]-domination number of tree.

• Journal of the Korean earth science society
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• v.32 no.6
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• pp.575-585
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• 2011

The effect of wavelet pair choice in the compression of the satellite images is studied. There is a trade-off between compression rate and perception quality. The encoding ratio is used to express the compression rate, and Peak Signal-to-Noise Ratio (PSNR) is also used for the perceptional performance. The PSNR and the encoding ratio are not matched well for the images with various wavelet pairs, but the tendency is remarkable. It is hard to find the pattern of PSNR for sampled images. On the other hand, there is a pattern of the variation range of the encoding ratio for each image. The satellite images have larger values of the encoding ratio than those of nature images (close range images). Depending on the wavelet pairs, the PSNR and the encoding ratio vary as much as 13.2 to 21.6% and 16.8 to 45.5%, respectively for each image. For Synthetic Aperture Radar (SAR) images the encoding ratio varies from 16 to 20% while for the nature images it varies more than 40% depending on the choice of wavelet pairs. The choice of wavelet for the compression affects the nature images more than the satellite images. With the indices such as the PSNR and the encoding ratio, the satellite images are less sensitive to the choice of wavelet pairs. A new index, energy concentration ratio (ECR) is proposed to investigate the effect of wavelet choice on the satellite image compression. It also shows that the satellite images are less sensitive than the nature images. Nevertheless, the effect of wavelet choice on the satellite image compression varies at least 10% for all three kinds of indices. However, the important of choice of wavelet pairs cannot be ignored.