• Journal of the Korea Institute of Information Security & Cryptology
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• v.11 no.6
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• pp.67-76
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• 2001

In this paper, we investigate criteria for evaluating cryptographic strength based on randomness testing of the advanced encryption standard candidates, which have conducted by NIST(National Institute of Standards & Technology). It is difficult to prove that a given cryptographic algorithm meets sufficient conditions or requirements for provable security. The statistical testing of random number generators is one of methods to evaluate cryptographic strength and is based on statistical properties of random number generators. We apply randomness testing on several cryptographic algorithms that have not been tested by NIST and find criteria for evaluating cryptographic strength from the results of randomness testing. We investigate two criteria, one is the number of rejected samples and the other is the p-value from p-values of the samples.

• Journal of Elementary Mathematics Education in Korea
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• v.20 no.4
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• pp.655-676
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• 2016

The purpose of this study is to examine the effects of teaching on functional thinking, one of the algebraic thinking in sixth grade students level. For this study, we developed functional thinking based-teaching through analyzing mathematical curriculum and preceding research, which consisted of 12 classes, and we investigated the effects of teaching through quantitative and qualitative analysis. In the results of this study, functional thinking based-teaching was statistically proven to be more effective in improving algebraic reasoning skills and lower elements which is an algebraic reasoning as generalized arithmetic and functional thinking, compared to traditional textbook-centered lessons. In addition, the functional thinking based-teaching gave a positive impact on the functional thinking level. Thus functional thinking based-teaching provides guidance on the implications for teaching and learning methods and study of the functional thinking in the future, because of the significant impact on the mathematics learning in six grade students.

• School Mathematics
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• v.15 no.3
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• pp.603-617
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• 2013

The major purpose of this article is to examine what kind of gap exists between mathematically gifted students' probability knowledge and the reality actually applying that knowledge and then analyze the cause of the gap. To attain the goal, 23 elementary mathematically gifted students at the highest level from G region were provided with problem situations internalizing a probability and expectation, and the problems are in series in which conditions change one by one. The study task is in a gaming situation where there can be the most reasonable answer mathematically, but the choice may differ by how much they consider a certain condition. To collect data, the students' individual worksheets are collected, and all the class procedures are recorded with a camcorder, and the researcher writes a class observation report. The biggest reason why the students do not make a decision solely based on their own mathematical knowledge is because of 'impracticality', one of the properties of probability, that in reality, all things are not realized according to the mathematical calculation and are impossible to be anticipated and also their own psychological disposition to 'avoid loss' about their entry fee paid. In order to provide desirable probability education, we should not be limited to having learners master probability knowledge included in the textbook by solving the problems based on algorithmic knowledge but provide them with plenty of experience to apply probabilistic inference with which they should make their own choice in diverse situations having context.

• Management & Information Systems Review
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• v.32 no.3
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• pp.107-125
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• 2013

This study deals with a strategic decision making in two level supply chain network design. This study presents more realistic mathematical model than the previous studies by considering simultaneous location of plants and distribution centers, determination of capacity level for both plants and distribution centers, and upper limit condition for numbers of locating plants and distribution centers. This paper tries to help the strategic decision making for two level supply chain network design. For this purpose, three different sized numerical examples are generated and optimal solutions are obtained by applying Excel Solver program. And sensitivity analysis is performed for the biggest sized example problem, which has 10 potential plants, 20 potential distribution centers, and 200 customer zones. After the plants being located are fixed, optimal minimum costs are obtained and compared for each of 7 different numbers of distribution centers to be located. As the number of distribution centers increases, changes in inbound transportation cost and outbound transportation cost can be derived. In case of considering cost as well as customer satisfaction level for two level supply chain network design, the analysis of this changes may help more sophisticated decision making.

• The Mathematical Education
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• v.48 no.3
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• pp.303-328
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• 2009

In this study, we developed the teaching methods using manipulative materials to teach regular polytopes, and applied these to first-year student of middle school who is attending the extra math class. In that class, we focused on the change of the mathematical representations -especially verval, visual and symbolic representations- and mathematical behavioral. By analyzing characterstics the students' work sheets, we obtained affirmative results as follows. First, manipulative materials played an important role on drawing a development figure of regular polyhtopes describing the verval representation definition of regular polytopes. Second, classes utilizing manipulative materials changed students verbalism level of representations the definition of regular polytopes. For example, in the first class about 60% of students are in the $0{\sim}2$ vervalism level, but in the third class, about 65% of students are in the $6{\sim}7$ level. Third, classes utilizing manipulative materials improved visual representation about development figure. After experiences making several development figures about regular octahedron directly, and discussion, students found out key points to be considered for draws development figure and this helped to draw development figures about other regular polytopes. Fourth, students were unaccustomed to make symbolic representations of regular polytopes. But, they obtained same improvement in symbolic representations, so in fifth the class some students try to make symbol about something in common of whole regular polytopes. Fifth, after the classes, we have significant differences in the students, especially behavioral characteristics in II items such as mind that want to study own fitness, interest, attachment, spirit of inquiry, continuously mathematics posthumously. This means that classes using manipulative materials. Specially, 'mind that want to study mathematics continuously' showed the biggest difference, and it may give positive influence to inculcates mathematics studying volition while suitable practical use of manipulative materials. To conclude, classes using manipulative materials may help students enhance the verbal, visual representation, and gestates symbol representation. Also, the class using manipulative materials may give positive influence in some part of mathematical behavioral characteristic. Therefore, if we use manipulative materials properly in the class, we have more positive effects on the students cognitive perspect and behavioral cteristics.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.11
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• pp.5841-5846
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• 2013

In this work, we consider the effect of doppler bandwidth on the performance of channel sounding. We develop the mathematical formulation of the problem and compare the MMSE channel estimator to the simple correlator. Examples of the performance of the MMSE and correlator estimators are presented for the single-input single-output (SISO) case with various values of Doppler bandwidth to assess the impact of time variation. The results show that as the $f_dT$ product increases the performance of both the MMSE and correlator estimates gets worse, and that the performance of the MMSE estimator improves relative to the correlator.We also consider case that the exact statistics of the channel are unknown It is shown that when the mismatch is not too large, the MMSE estimator with mismatch still does better than the simple correlator, but if the mismatch is large, then the correlator can do better.

• Proceedings of the Korea Multimedia Society Conference
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• 2000.11a
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• pp.419-422
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• 2000

본 논문에서는 길을 기반으로 하여 학습자 스스로 학습의 장면을 결정하고, 학습의 형태를 계획하여 학습을 주도적으로 이끌어 낼 수 있도록 하는 학습자 중심의 자기주도적 학습 환경을 선계 및 구현하였다. 학습 설계 대상은 학습자와 길 사이의 동적 상호작용을 통하여 지필 학습방법으로 학습하기 힘들었던 단원인 고등학교 공통수학의 삼각함수를 선택하였다. 학습자가 학습장면에서 직접 실행해 보고 도형을 이동시켜 변화하는 현상을 관찰하고 탐구함으로써 실시간으로 피드백이 가능하여 학습의 효과를 극대화하였으며 학습자에 대한 정보와 학습의 상태는 DB를 이용하여 관리하도록 하였고 형성평가와 총괄평가는 DB를 이용하도록 설계하였다.

• Proceedings of the Korean Information Science Society Conference
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• 2012.06a
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• pp.419-421
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• 2012

본 논문에서는 유전 프로그래밍에 기반하여 복잡한 주가지수를 예측함에 있어 사칙연산만을 사용하여 유전 프로그래밍을 구현하는 실험을 소개한다. 전통적인 방법의 주가지수 예측은 적용 분야에 대한 전문 지식과 복잡한 수학적 연산을 요구하여 구현의 어려움과 수행 속도에 문제가 있었다. 본 논문에서는 적용 분야의 전문지식에 의존하지 않는 유전 프로그래밍과 빠른 연산속도의 사칙연산만을 사용하여 이러한 문제점을 극복하는 전략을 사용하였다. 제안된 전략은 실험 결과를 통해 실제 주가지수 변화에 상당히 근접함을 확인하였다.

• The Journal of the Acoustical Society of Korea
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• v.7 no.4
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• pp.110-116
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• 1988

The thermal front over the shallow coastal seas of Korea during the winter season provides very unique acoustic media such that wave equation is easily separable and the solutions turn out to be very simple and well known. In steady of using the WKB method to solve the radial equation the mode technique have been applied to obtain the solution. The radial propagation is rather weakly influenced by the presence of the thermal front that causes the horizontal variations of the sound speed. The physical description of the sound propagation is also presented in terms of ray tracing.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.19 no.6
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• pp.731-738
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• 2010

Cavitation is described by formation and collapse of the bubbles in a liquid when the ambient pressure decreases. Formed bubbles grow and collapse by change of pressure, and when they collapse, shockwave by high pressure is generated. In general, bubble behavior can be described by Rayleigh-Plesset equation under adiabatic or isothermal condition and hence, phase shift by the pressure change in a bubble cannot be considered in the equation. In our study, a numerical model is developed from the mathematical model considering the phase shift from the previous study. In the developed numerical model, size of single spherical bubble is calculated by the change of mass calculated from the change of the ambient pressure in a liquid. The developed numerical model is verified by a case of liquid flow in a narrow channel.