• Journal of the Korean School Mathematics Society
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• v.15 no.2
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• pp.259-279
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• 2012

The purposes of this study were to investigate the effects of the use of link sheet in pre-service mathematics teachers' mathematics learning. The study was conducted in Calculus course during 1 semester with 25 pre-service mathematics teachers. According to the results of questionnaires and focused group interviews, the use of the link sheet helped students to develop deeper understandings of mathematical concepts and mathematical communication ability. In addition, the use of the link sheet encouraged students to realize the value of the mathematics and it also played a central role in creating active and self-directed learning atmosphere.

• Journal of Educational Research in Mathematics
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• v.8 no.2
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• pp.753-762
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• 1998

This Paper reports results of investigating the relationship between students' perfoonance and mathematics imtructiooal system in understanding of the function concept. A written examination measuring calcullli students' understanding of the fimction concept was administered to two groups of students whose educatiooal oockground were different. One group consists of students who completed a pre-calculus course in Korea and the other group completed the same course in the United States. This study investigates how students in two groups acquire an understanding of major aspects of the function concept and provided interesting insights regarding the different background and belief related to their performance. Follow-up interviews were conducted to identify possible explanations for the different performance of the two groups in understanding the function concepts. Results indicate that the differences came from the educational environment and individual belief.

• Communications of Mathematical Education
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• v.33 no.2
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• pp.47-66
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• 2019

The purpose of this study is followings. First, we develop and apply teaching and learning methods for conducting team projects in flipped calculus class. Second we collect data such as team reports, individual reviews, and surveys during class activities. Third we survey the impacts on participation in student team activities, advanced studying, communication and collaboration. A total of 120 engineering and science majoring students participated in the 16-week long class study administered in team project learning styles in Spring 2018. There were two characteristics of this class. First students studied concepts and examples with video in pre-class and did the team project learning in the classroom. Second we used Google Drive to record team project progress, and to make sure the instructor to intervene appropriately in team activities. We conducted a team project inside and outside the classroom. This could lead the instructor to advise students and so their participation in team activity increased. As a result, it not only had a good effect on communication and cooperation, but also had an effect on advanced learning.

• Journal of Information Processing Systems
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• v.6 no.3
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• pp.335-346
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• 2010

The present study investigates the difficulty of solving the mathematical problem, namely the DLP (Discrete Logarithm Problem) for ephemeral keys. The DLP is the basis for many public key cryptosystems. The ephemeral keys are used in such systems to ensure security. The DLP defined on a prime field $Z^*_p of random prime is considered in the present study. The most effective method to solve the DLP is the ICM (Index Calculus Method). In the present study, an efficient way of computing the DLP for ephemeral keys by using a new variant of the ICM when the factors of p-1 are known and small is proposed. The ICM has two steps, a pre-computation and an individual logarithm computation. The pre-computation step is to compute the logarithms of a subset of a group and the individual logarithm step is to find the DLP using the precomputed logarithms. Since the ephemeral keys are dynamic and change for every session, once the logarithms of a subset of a group are known, the DLP for the ephemeral key can be obtained using the individual logarithm step. Therefore, an efficient way of solving the individual logarithm step based on the newly proposed precomputation method is presented and the performance is analyzed using a comprehensive set of experiments. The ephemeral keys are also solved by using other methods, which are efficient on random primes, such as the Pohlig-Hellman method, the Van Oorschot method and the traditional individual logarithm step. The results are compared with the newly proposed individual logarithm step of the ICM. Also, the DLP of ephemeral keys used in a popular password key exchange protocol known as Chang and Chang are computed and reported to launch key recovery attack.

• Communications of Mathematical Education
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• v.22 no.4
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• pp.417-444
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• 2008

Many research papers on the college students' functional concept show they have poor understanding on this topic. To compare the results with that of Korean students, four interrelated topics are chosen: How do they understand the concept of function?; what are their misconceptions including epistemological obstacles?; How do the function concepts develop and are acquired? For this a survey has been conducted to 95 engineering students just before they start Calculus course. We have done research on other major areas including psychology, economics and statistics to see how function is defined in these areas. Function definitions from US math text books are also introduced. Based on the these and the survey, some suggestions are made on the new curriculum which treat function as a correspondence relation. Vertical line test should be added to the Algebra II/Pre calculus course to check the univalent property.

• Advances in Computational Design
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• v.2 no.2
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• pp.107-119
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• 2017

The Micro circular diaphragm (MCD) is the mechanical actuator part used in the micro electro-mechanical sensors (MEMS) that combine electrical and mechanical components. These actuators are working under harsh mechanical and thermal conditions, so it is very important to study the mechanical and thermal behaviors of these actuators, in order to do with its function successfully. The objective of this paper is to determine the thermo-mechanical behavior of MCD by developing the traditional bulge test technique to achieve the aims of this work. The specimen is first pre-stressed to ensure that is no initial deflection before applied the loads on diaphragm and then clamped between two plates, a differential pressure (P) and temperature ($T_b$) is leading to a deformation of the MCD. Analytical formulation of developed bulge test technique for MCD thermo-mechanical characterization was established with taking in-to account effect of the residual strength from pre-stressed loading. These makes the plane-strain bulge test ideal for studying the mechanical and thermal behavior of diaphragm in both the elastic and plastic regimes. The differential specimen thickness due to bulge effect to describe the mechanical behavior, and the temperature effect on the MCD material properties to study the thermal behavior under deformation were discussed. A finite element model (FEM) can be extended to apply for investigating the reliability of the proposed bulge test of MCD and compare between the FEM results and another one from analytical calculus. The results show that, the good convergence between the finite element model and analytical model.

• The Journal of the Korea Contents Association
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• v.17 no.6
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• pp.81-85
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• 2017

The aim of this study was to evaluate the usability of applied Low dose Computed Tomography(LDCT) protocol in examining urinary calculus using computed tomography. The subjects of this study were urological patients who visited a medical institution located in Busan from June to December 2016 and the protocol used in this study was Adaptive Statistical Iterative Reconstruction: low-dose CT with 50% Adaptive Statistical Iterative Reconstruction (ASIR). As results of quantitative analysis, the mean pixel value and standard deviation within kidney region of image(ROI)of the axial image were $26.21{\pm}7.08$ in abdomen CT pre scan and $20.03{\pm}8.16$ in low-dose CT. Also the mean pixel value and standard deviation within kidney ROI of the coronal image were $22.07{\pm}7.35$ in abdomen CT pre scan and $21.67{\pm}6.11$ in low dose CT. The results of qualitative analysis showed that four raters' mean values of observed kidney artifacts were $19.14{\pm}0.36$ when using abdomen CT protocol and $19.17{\pm}0.43$ in low-dose CT, and the mean value of resolution and contrast was $19.35{\pm}0.70$ when using abdomen CT protocol and $19.29{\pm}0.58$ in low-dose CT. Also the results of a exposure dose analysis showed that the mean values of CTDIvol and DLP in abdomen CT pre scan were 18.02 mGy and $887.51mGy{\cdot}cm$ respectively and the mean values of CTDIvol and DLP when using low-dose CT protocol were 7.412 mGy and $361.22mGy{\cdot}cm$ respectively. The resulting dose reduction rate was 58.82% and 59.29%, respectively.

• Proceedings of the KIEE Conference
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• 1991.11a
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• pp.361-365
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• 1991

The problem being considered here is the determination of optimal guidance laws for a launch vehicle for scientific missions. The optimal guidance commands are determined in the sense that the least amount of fuel is used. A numerical solution was obtained for the case where the position and velocity state variables satisfy a specified constraint at the time of thrust cutoff. The method used here is based on the Pontryagin's maximum principle. This is the method of solving a problem in the calculus of variations. In particular, it applies to the problem considered here where the magnitude of the control is bounded. Simulations for the optimal guidance algorithm, during the 2nd and the 3rd-stage flight of the Japanese rocket M-3H-3, are carried out. The results show that the guided trajectory that satisfying the terminal constraints is optimal, and the guidance algorithm works well in the presence of some errors during the 1st-stage pre-programmed guidance phase.

• Journal of Korean society of Dental Hygiene
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• v.17 no.6
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• pp.983-992
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• 2017

Objectives: This study is to compare measuring gingival and peridontal indices and changes in dental plaque per period using a three mix types of dentifrice and to investigate dental diseases preventive effects depending on gingivitis reducing effect of dentifrice through a clinical experiment. Methods: This study targeted adult females and males with mild to moderate gingivitis from age 20 to 60. The Calculus index, Papillary Marginal Attached Gingival (PMA) index, Gingival index, Patient Hygiene Performance (PHP) index, and Plaque index were measured at pre-experiment and at 1, 2, 4 weeks post experiment. Results: The PMA, Gingival index, PHP index, plaque index of experimentla group decreased after 4 weeks (p<0.05). Conclusions: A three mix types of dentifrice for relieving tooth sensitivity was verified to be effective in removing dental plaque and reducing gingivitis.

• International Journal of Oral Biology
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• v.40 no.2
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• pp.93-101
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• 2015

The efficacy of air-polishing on subgingival debridement, as compared to scaling and root planning (SRP), was evaluated clinically and microbiologically. Fifteen patients diagnosed as chronic periodontitis, and having single-root tooth over 5 mm of pocket depth symmetrically in the left and right quadrant, were investigated. Subgingival debridement was performed by SRP and air-polishing. The results were evaluated and compared clinically and microbiologically. Probing pocket depth (PPD), bleeding on probing (BOP), relative attachment level (RAL) and change of gingival crevicular fluid (GCF) were assessed before treatment, and at 14 and 60 days after treatment. Microbial analysis was done pre-treatment, post-treatment, and at 14 and 60 days after treatment. Results of air polishing showed that post treatment, the PPD and BOP decreased, and attachment gain was observed. There was no clinical difference when compared to SRP. The volume of GCF decreased at 14 days, and increased again at 60 days. Compared to SRP, there was a statistical significance of the volume of GCF at 60 days in air-polishing. In the microbial analysis, high-risk bacteria that cause periodontal disease were remarkably reduced. They decreased immediately after treatment, but increased again with the passage of time. Thus, our results show that subgingival debridement by air-polishing was effective for decrease of pocket depth, attachment gain, decrease of GCF and inhibition of pathogens. Further studies are required to compare air-polishing and SRP, considering factors such as degree of pocket depth and calculus existence.