• Proceedings of the Korean Operations and Management Science Society Conference
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• 2005.10a
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• pp.321-333
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• 2005

With the limited frequency spectrum and an increasing demand for cellular communication services, the problem of channel assignment becomes increasingly important. However, finding a conflict free channel assignment with the minimum channel span is NP hard. As demand for services has expanded in the cellular segment, sever innovations have been made in order to increase the utilization of bandwidth. The innovations are cellular concept, dynamic channel assignment and hierarchical network design. Hierarchical network design holds the public eye because of increasing demand and quality of service to mobile users. We consider the frequency assignment problem and the base station placement simultaneously. Our model takes the candidate locations emanating from this process and the cost of assigning a frequency, operating and maintaining equipment as an input. In addition, we know the avenue and demand as an assumption. We propose the network about the profit maximization. This study can apply to GSM(Global System for Mobile Communication) which has 70% portion in the world. Hierarchical network design using GA(Genetic Algorithm) is the first three-tier (Macro, Micro, Pico) model, We increase the reality through applying to EMC (Electromagnetic Compatibility Constraints). Computational experiments on 72 problem instances which have 15${\sim}$40 candidate locations demonstrate the computational viability of our procedure. The result of experiments increases the reality and covers more than 90% of the demand.

• Proceedings of the IEEK Conference
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• 2002.06e
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• pp.9-12
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• 2002

The problem of sub-Nyquist nonuniform sampling for the perfect reconstruction of signals with time-varying spectral contents is studied. The signals are assumed to have a known instantaneous bandwidth in time-frequency domain. As the function of time, the nonuniform sampling pattern of a given signal, that is, the instantaneous sampling frequency is determined by the observation of instantaneous bandwidth based on time-frequency analysis. The proposed sampling pattern guarantees the perfect reconstruction of nonuniform sampled signals under Nyquist-sampling rate in average.

• Korean Journal of Child Studies
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• v.14 no.2
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• pp.49-63
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• 1993

The purpose of this study was to investigate the effects of problem solving interaction through puppetry on interpersonal problem solving thinking. The subjects were 60 children, ranging in age from 69 to 72 months. All subjects were randomly assigned to one of three experimental groups: the control group with no treatment, the puppetry group, the puppetry problem solving interaction group. The treatment covered 4 weeks. The instrument was based on Shure and Spivack's(1974) Preschool Interpersonal Problem Solving (PIPS) test. The data were analyzed with paired t-test, one-way ANOVA, Tukey test, percentage, and Kendall's ${\tau}$. There were significant differences among the three groups in the frequency of solving interpersonal problems. The problem solving interaction with puppetry group was the most effective on Interpersonal Cognitive Problem Solving Strategies. These results showed that problem solving interaction with puppetry is effective in cultivating young children's interpersonal problem solving thinking.

• The Journal of the Korea Contents Association
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• v.21 no.5
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• pp.435-445
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• 2021

Recently, gambling problem of youth has seriously increased. the aim of this study is to investigate the effect of sociodemographic and gambling characteristics on the future gambling participation intention among middle school students. Analysis through chi-square test and logistic regression was conducted using data from 10,228 middle school students collected in the 2018 Survey on Youth Gambling problems given from Korea center on Gambling problems. The research findings were as follows. First, among the demographics factors, sex, grade, allowance and parents-children communication showed significant difference on future gambling participation intention. Second, among the gambling factors, awareness of gambling seriousness and spending, frequency, time, cost, chasing behavior, problem gambling level showed significant difference on future gambling participation intention. Third, grade, awareness of gambling seriousness, gambling frequency, chasing behavior, problem gambling predicted the occurrence of future gambling participation intention. Based on these results, the present study suggests the prevention and intervention of gambling problem among middle school students.

• 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.

• Journal of the Institute of Electronics Engineers of Korea CI
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• v.46 no.4
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• pp.51-60
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• 2009

In radio frequency identification(RFID) systems, when an RFID reader uses the same or adjacent frequency with neighbor readers, the interference between the readers may occur, which causes the reader collision and errors in tag recognition. In the previous study on RFID reader anti-collision, the techniques based on Frequency Division Mutiplex(FDM) or Time Division Multiplex(TDM) are proposed. However in these paper, the problem on the condition of RFID reader-to-reader interference considering the distance between interfering readers, frequency and operating time is not define exactly. In this paper, the interference effect is analyzed through RFID reader interference model considering the TDM and FDM, and the optimization problem is defined. To solve this, genetic-resource allocation technique is proposed. Therefore the optimal resource allocation applied RFID environment faithfully is accomplished.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1998.04a
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• pp.492-497
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• 1998

Thermoacoustic oscillation is a significant problem in cylindrical-type combustors such as common internal combustion engines, industrial furnaces, gas turbine, etc. This kind of low frequency oscillation can give rise to serious troubles such as the destruction of system or producing of a strong noise. Accurate numerical simulation of thermoacoustic phenomena is a complex and challenging problem. Especially, considering the reaction of mixture intensifies the difficulty of analysis. Like as other simulations of the aerodynamics and aeroacoustics, direct computation of thermoacoustic phenomena requires that the Navier-Stokes equations be solved using accurate numerical differentiation and time-marching schemes, with non-reflecting boundary conditions. In this study,, numerical approach aims at qualitative analysis and efficient prediction of problem, not at the development of an accurate scheme. Overally speaking, numerical prediction is reasonably matched with experimental result.

• Journal of The Korean Association For Science Education
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• v.15 no.4
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• pp.452-458
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• 1995

Science textbooks are very important materials in order to know elementary science learning in Japan and Korea. In this research the 5th grade science textbooks in Japan and Korea are analyzed by an analyzing category. The analyzing category is consisted of knowledge and scientific inquiry. Knowledge is divided by fact, concept, and rule. Scientific inquiry is divided by problem cognition, variable control, experiment planning, observing, measuring, categorizing, inferring, data transformation, predicting, correlation, cause and effect, result, communication, which are 13 subcategories. Analyzing methods are counting the frequency of each subcategory and tabulating the data. The results of this study are: 1. The frequency of scientific inquiry appeared in Korean 5th grade science textbooks is three times more than that in Japanese textbooks. 2. In scientific inquiry category, Japanese science textbooks emphasized observing, predicting, measuring and problem cognition; Korean science textbooks emphasized experiment planning, observing and problem cognition. 3. In knowledge category, fact subcategory is mostly emphasized in both countries.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.05a
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• pp.385-392
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• 2001

Time-dependent frequency and energy of free vibration of the Spagetti problem, that is the axially moving continuum with time-varying length, are investigated. Exact expressions for the natural frequency and time-varying vibration energy are derived by dealing with traveling waves. When the string length is increased, the vibration period increases, but the free vibration energy varies as a function of both translating velocity and boundary velocity of the continuum. However, when the string undergoes retraction, the vibration energy increases with time, String tension together with non-zero instantaneous velocity at the moving boundary results in energy variation.

• 제어로봇시스템학회:학술대회논문집
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• 1995.10a
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• pp.340-343
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• 1995

In this paper, we get a reduced order controller in $H^{\infty}$ mixed sensitivity problem with weighting functions. For this purpose, we define frequency weighted coprime factor of plant in $H^{\infty}$ mixed sensitivity problem and reduce the coprime factor using the frequency weighted balanced truncation technique. The we design the controller for plant with reduced order coprime factor using J-lossless coprime factorization technique. Using this approach, we can derive the robust stability condition and achieve good performance preservation in the closed loop system with reduced order controller. And it behaves well in both stable plant and unstable plant.t.