• Research in Mathematical Education
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• v.14 no.3
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• pp.263-279
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• 2010

Teachers' personal knowledge (PK) is an element in their pedagogic-practical knowledge. This study exposes the PK of primary school mathematics teachers regarding solid geometry through reflection. Students are exposed to solid geometry on various levels, from kindergarten age and above. Previous studies attested to the fact that students encounter difficulties-strong dislike and fear engendered by geometry. A good number of teachers have strong dislike to solid geometry, as well. Therefore, those engaged in teaching the subject must address the problem and try to overcome these difficulties. In this paper we have introduced the reflective process among teachers in primary school, including application of Van-Hiele's theory to solid geometry.

• Journal of computational fluids engineering
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• v.10 no.1
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• pp.99-106
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• 2005

Performance of first, second and third order accurate methods for calculation of in viscid fluxes in fluid flow governing equations are investigated here. For the purpose, an upwind method based on Roe's scheme is used to solve 2-dimensional Euler equations. To increase the accuracy of the method two different schemes are applied. The first one is a second and third order upwind-based algorithm with the MUSCL extrapolation Van Leer (1979), based on primitive variables. The other one is an upwind-based algorithm with the Chakravarthy extrapolation to the fluxes of mass, momentum and energy. The results show that the thickness of shock layer in the third order accuracy is less than its value in second order. Moreover, applying limiter eliminates the oscillations near the shock while increases the thickness of shock layer especially in MUSCL method using Van Albada limiter.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.16 no.2
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• pp.103-107
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• 2004

Empirical equation has been developed by employing the new non-dimensional physical number 'wave action slope' for the estimation of breakwater armor weight. Van der Meer(1987) introduced Iribarren number for the same purpose, but his equation shows very different trend of distribution with the condition of Iribarren number. On the other hand the equation related with wave action slope keeps the same trend of distribution over the whole region. When the parameter is related to the Iribarren number, the equation of wave action slope has a very high accuracy.

• Proceedings of the CALSEC Conference
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• 2005.03a
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• pp.149-154
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• 2005

Recently, lots of EDI-VAN (Electronic Data Interchange-Value Added Network) companies challenge to convert their business systems into Web-based e-business frameworks to avoid high cost and closed structure of EDI system. This research proposes e-Transformation strategies for EDI-VAN companies to adopt Web-based e-business standard frameworks such as ebXML (e-business using XML) and RosettaNet. Four migration strategies for EDI companies are presented, and their properties are described in detail. Transformation procedures of two representative strategies are also provided fur the convenience of medium-sized companies. The result of this work can be used as a practical guideline for EDI companies to develop there own transformation strategy suitable to its scale and capability, while minimizing the impacts on the pre-existing business processes.

• Journal of the Korean Chemical Society
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• v.56 no.5
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• pp.548-555
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• 2012

Ultrasonic velocity and density measurements have been undertaken for a number of binary liquid mixtures involving different commercial solvent extractants, LIX reagents. The binary mixtures under investigation have been classified under two categories such as polar-polar, and polar-non-polar types. Different theories and relations such as Schaaff's Collision Factor Theory (CFT), Nomoto's relation (NOM), and Van Dael & Vangeel ideal mixing relation (IMR) have been used to evaluate the velocity theoretically for all these binary systems. The relative merits of afore-mentioned theories and relations compared to experimental values of velocity have been discussed in terms of percentage variations. However, the CFT and Nomoto's relation show better agreement with the experimental findings than the ideal mixing relation for all the systems under investigation.

• Journal of the Korea Institute of Military Science and Technology
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• v.3 no.2
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• pp.219-230
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• 2000

Plastic bonded explosive(PBX) is mainly composed of the nitramine explosives, RDX, HMX, and polymer binders. When the adhesion between nitramine crystals and binder is not particularly strong and can be failed under stress, dewetting occurs rather suddenly and this leads to a significant drop in tensile strength of explosives. Mechnical property of plastic bonded explosive depends on the surface characteristics of filler and binder. In order to design for better adhesion, an understanding of the surface properties of explosive and binder is essential. In this study, 2 kinds of RDX and 4 kinds of ethylene vinyl acetate copolymers are selected, since they are widely used in many plastic bonded explosives. The technical objective of this investigation is to calculate for the surface free energy of RDX and EVA using theory of Fowkes, van Oss, Neumann approaches and Kaelble equation and to predict the interaction between filler and binder from their surface free energies.

• Bulletin of the Korean Chemical Society
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• v.34 no.1
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• pp.249-251
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• 2013

• Journal of the Korean Society of Safety
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• v.28 no.1
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• pp.35-39
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• 2013

The flash point is an important indicator of the flammability of a chemical. In this study, the flash points for the n-propanol+n-butanol and n-propanol+acetic acid systems were measured by Tag open-cup apparatus. The experimental data were compared with the values calculated by the Raoult's law and optimization method based on van Laar and UNIQUAC equations. The calculated values by optimization method were found to be better than those based on the Raoult's law.

• Proceedings of the KIEE Conference
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• 2006.07c
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• pp.1388-1389
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• 2006

금속의 전기비저항 측정은 4단자 방법, van der Pauw 방법, Four Point Probe(FPP) 방법 등이 있으며, 이들의 정확한 측정방법을 고찰하고, 그 중 FPP 방법에 의한 비저항의 두께효과를 비교 분석하기 위하여 비자성 금속 SUS 316을 두께별로 가공한 후 실험하였다. 그 결과 4단자 및 van der Pauw 방법으로 측정된 도전율은 각각 2.273 %IACS으로 나타났으며, FPP방법으로 측정된 도전율은 probe spacing 5.0 mm, dc current 10 A에서 시료의 두께가 2 mm일 때 2.288 %IACS, 3 mm일 때 2.271 %IACS로서 상기 두 방법으로 측정한 결과와 0.5 %이내에서 일치하였으나, 시료가 5mm 및 11 mm 에서는 매우 큰 오차를 나타냈다.

• The Mathematical Education
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• v.34 no.2
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• pp.141-202
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• 1995

van Hiele의 사고수준 이론에는 기초수존, 제1수준, 제2수준, 제3수준, 제4수준 등 5가지가 있고, 이 중에서 국민학교에 해당되는 것은 기초수준 (1학년), 제1수준(2, 3학년), 제2주순 (4, 5, 6학년) 등 세 가지 뿐이다. 그리고 기하학적의 구조 인식론에는 관제, 구성, 정의, 공리, 정리, 증명, 척도, 자호, 응용 등 9가지 단계가 있고, 이 9가지 단계를 기초수준, 제 1수준, 제 2수준의 각 수준에 대응시켜서 거기에 해당되는 기하도형 학습을 연구·분석하였다. 기하도형에 관한 학습은 주로 경험성과 창의성을 바탕으로 하는 보기문제를 제시하여 그 흐름을 해결함으로써 각 수준의 각 단계들을 스스로 인식하도록 하였다. 특히 여기에서 처음으로 등장하는 기하학의 구조 인식론이라는 것은 위에서 언급한 9가지 단계를 차례로 거쳐 가야만 아동들은 도형을 올바르게 빠짐없이 인식할 수 있다는 이론이다. 이 이론의 특징을 예를 하나 들어서 설명해 보면, 흔히들 정의를 단순히 무정의어와 정의어로 구분하고 있는데 반하여, 이 이론에서는 서로 역동적인 관계를 갖고 있는 기초정의, 상황정의, 포괄정의, 기본정의, 부수정의, 특수정의 등으로 나누었다는 점이다.