• Journal for History of Mathematics
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• v.18 no.4
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• pp.113-124
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• 2005

For a Tychonoff space X, C(X) is a Riesz-space. It is well known that C(X) is order-Cauchy complete if and only if X is a quasi~F space and that if X is a compact space and QF(X) is a minimal quasi-F cover of X, then the order- Cauchy completion of C(X) is isomorphic to C(QF(X)). In this paper, we investigate motivations and historical backgrounds of the definition for quasi-spaces and the construction for minimal quasi-F covers.

• The Journal of the Acoustical Society of Korea
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• v.25 no.8
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• pp.356-361
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• 2006

We present the performance of differential space-time block decoders. which does not require the channel state information. We suggest the structure of the multiple blocks differential space time decoders. which does not require the channel state information, and analyze the Performances. In quasi-static flat fading channels. the Performance of multiple blocks differential detection (MD-STC) outperforms that of 2 blocks(D-STC) by 1.5dB. But in the time-selective fading channels due to Doppler frequency $(f_d)$, the performance of MD-STC degrades as the vehicular speed is greater than 200km/hr in 802.16e systems, where the data transmission rate is 144kbps.

• Journal of Elementary Mathematics Education in Korea
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• v.11 no.2
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• pp.117-136
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• 2007

The purpose of this study was to analyze the effects of mathematics learning through tessellation activities on the improvement of spatial sense and to find out a better mathematics teaching method that could further develop spatial sense. For this purpose, the following questions were attempted; Can mathematics learning using tessellation activities develop spatial sense? In odor to test this hypothesis, twenty-four fifth graders of a class were selected at random. And the experimental group was divided into four groups according to gender and academic performance. The groups were protested and post-tested to determine results based on the quasi-experimental design(i.e. one-group pretest-post test design). The process of this study was checking spatial sense for a common evaluation of experimental group. In this study, tangram, pattern block, and GSP was used for mathematics learning through tessellation activities during each independent-study, discretion-activity, and math class. The instrument used in this study was a spatial sense test and pretest and post-test were implemented with the same instrument(i.e. K-WISC-III Activity Test). In conclusion, mathematics learning through tessellation activities with tangram, pattern block, and GSP is an effective teaching and learning method for the improvement of the spatial sense.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.5
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• pp.1158-1167
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• 1995

In this study, the dynamic instabilities of a beam, subjected to periodic short impulsive loading, are investigated using simple 2-DoF beam model. The behaviors of beam model whose axial motions are constrained are studied for the case of elastic and elastic-plastic behavior. In the case of elastic behavior, the chaotic responses due to the periodic pulse are identified, and the characteristics of the behavior are analysed by investigating the fractal attractors in the Poincare map. The short-term and long-term responses of the beam are unpredictable because of the extreme sensitivities to parameters, a hallmark of chaotic response. In the case of elastic-plastic behavior, the responses are governed by the plastic strains which occur continuously and irregularly as time increases. Thus the characteristics of the response behavior change continuously due to the plastic strain increments, and are unpredictable as well as the elastic case.