• Journal of Mechanical Science and Technology
• /
• 제20권11호
• /
• pp.1891-1897
• /
• 2006

In this study, a new model to predict the effective elastic constants of composites with spherical fillers is proposed. The original Eshelby model is extended to a finite filler volume fraction without using Mori-Tanaka's mean field approach. When single filler is embedded in the matrix, the effective elastic constants of the composite are computed. The composite is in turn considered as a new matrix, where new single filler is again embedded in the matrix. The predicted results by the present model with a series of embedding procedures are compared with those by Mori-Tanaka, self-consistent, and generalized self-consistent models. It is revealed through parametric studies such as stiffness ratio of the filler to the matrix and filler volume fraction that the present model gives more accurate predictions than Mori-Tanaka model without using the complicated numerical scheme used in self-consistent and generalized self-consistent models.

• 한국수학교육학회지시리즈A:수학교육
• /
• 제48권3호
• /
• pp.235-263
• /
• 2009

The purpose of the study was to investigate the influence of children's understanding of fractions in mathematics problem solving. Kieren has claimed that the concept of fractions is not a single construct, but consists of several interrelated subconstructs(i.e., part-whole, ratio, operator, quotient and measure). Later on, in the early 1980s, Behr et al. built on Kieren's conceptualization and suggested a theoretical model linking the five subconstructs of fractions to the operations of fractions, fraction equivalence and problem solving. In the present study we utilized this theoretical model as a reference to investigate children's understanding of fractions. The case study has been conducted with 6 children consisted of 4th to 5th graders to detect how they understand factions, and how their understanding influence problem solving of subconstructs, operations of fractions and equivalence. Children's understanding of fractions was categorized into "part-whole", "ratio", "operator", "quotient", "measure" and "result of operations". Most children solved the problems based on their conceptual structure of fractions. However, we could not find the particular relationships between children's understanding of fractions and fraction operations or fraction equivalence, while children's understanding of fractions significantly influences their solutions to the problems of five subconstructs of fractions. We suggested that the focus of teaching should be on the concept of fractions and the meaning of each operations of fractions rather than computational algorithm of fractions.

• 한국자동차공학회논문집
• /
• 제18권3호
• /
• pp.26-36
• /
• 2010

This paper provides a description of the combustion model to obtain an accurate dynamic engine phenomena that satisfies real-time simulation for model-based engine control. The combustion chamber is modeled as a storage device for mass and energy. The combustion process is modeled in terms of a two-zone model for the burned and unburned gas fractions. The mass fraction burnt is modeled in terms of a Wiebe function. The instantaneous net engine torque is calculated from the engine speed and the instantaneous piston work. The modeling accuracy has been tested with a cylinder pressure data on a test bench and also the ability of real-time simulation has been checked. The results show that combustion model yields sufficiently good performance for the model-based control logic design. However the influence factors effected on model accuracy are some room for improvement.

• 한국수학교육학회지시리즈C:초등수학교육
• /
• 제7권1호
• /
• pp.31-41
• /
• 2003

Representation has been main topic in teaching and learning mathematics for a long time. Moreover, teachers' deficiency of representation about fraction results in teaching algorithms without conceptual understanding. So, this paper was conducted to investigate and analysize the elementary preservice mathematics teachers' representation about fraction. 38 elementary preservice mathematics teachers participated in this study. This study results showed that, the only model of a fraction that was familiar to the preservice teachers was the part of whole one. And research showed that, they solved the problems about fraction well using algorithms but seldom express the sentence which illustrates the meaning of the operation by a fraction. Specially, the division aspect of a fraction was not familiar nor readily accepted. It menas that preservice teachers are used to using algorithms without a conceptual understanding of the meaning of the operation by a fraction. This results give us some implications. Most of all, teaching programs in preservice mathematics teachers education have to devise to form a network among the concepts in relation to fraction. And we must emphasize how to teach and what to teach in preservice mathematics teachers education course. Finally, we have to invent the various materials which can be used to educate both preservice teachers and elementary school students. If we want to improve the mathematical ability of students, we will concentrate preservice teachers education.

• 생약학회지
• /
• 제54권2호
• /
• pp.66-71
• /
• 2023

Ethyl acetate (EA) soluble fraction of the Berberis amurensis (Berberidaceae) methanol extract showed the potent DPPH radical scavenging activity through Caenorhabditis elegans model system. The EA fraction was measured for the activity of superoxide dismutase (SOD), catalase, and oxidative stress tolerance by using C. elegans along with reactive oxygen species (ROS) level. In addition, SOD-3 expression was conducted using a transgenic strain (CF1553) to confirm that the regulation of the stress response gene is responsible for the increased stress tolerance of C. elegans treated by the EA fraction. As a result, the EA soluble fraction of B. amurensis increased SOD and catalase activity, and decreased ROS accumulation in a dose-dependent manner. Furthermore, the EA fraction-treated CF1553 worm showed higher SOD-3::GFP intensity than the control worm.

• 대한조선학회논문집
• /
• 제48권3호
• /
• pp.275-280
• /
• 2011

In the present study, a unified viscoplastic-damage model has been applied in order to describe the mechanical characteristics of fresh water ice such as nonlinear material behavior and volume fraction. The strain softening phenomenon of fresh water ice under quasi-static compressive loading has been evaluated based on unified viscoplastic model. The material degradation such as growth of slip/fraction has quite close relation with material inside damage. The volume fraction phenomenon of fresh water ice has been identified based on volume fraction (nucleation and growth of damage) model. The viscoplastic-damage model has been transformed to the fully implicit formulation and the discretized formulation has been implemented to ABAQUS user defined subroutine (User MATerial: UMAT) for the benefit of application of commercial finite element program. The proposed computational analysis method has been compared to uni-axial compression test of fresh water ice in order to validate the compatibilities, clarities and usefulness.

• 한국수학교육학회지시리즈C:초등수학교육
• /
• 제19권4호
• /
• pp.277-289
• /
• 2016

수학에서 다루는 개념적 지식과 절차적 지식의 연결은 중요하다. 개념적인 이해 없이 절차적 지식만을 강조하게 되면 무의미하게 알고리즘만을 반복적으로 수행할 가능성이 높기 때문이다. 이 글에서는 대분수와 가분수의 의미있는 상호 변환 과정을 강조하기 위하여 우리나라와 외국교과서에 제시된 대분수의 정의 방식과 대분수와 가분수의 상호 변환 내용을 분석하였다. 분석 결과, 우리나라와 외국의 교과서에서 대분수와 가분수의 변환 과정에서 분수 모델을 이용한 변환과 덧셈식을 활용한 변환으로 차이가 있는 것으로 나타났다. 분석 결과를 통해 대분수와 가분수에 대한 개념적 이해와 대분수와 가분수의 상호 변환과정에서 대분수의 수학적 의미를 바탕으로 학생 스스로 이들의 변환 과정에 대한 알고리즘을 발견할 수 있도록 교과서 내용을 재구성할 필요성을 제안하였다.

• 한국유체기계학회 논문집
• /
• 제18권4호
• /
• pp.49-55
• /
• 2015

The pumped storage plant operates with quick change of the discharge as well as quick changes between pump mode and turbine mode. This study focuses on the cavitation analysis of a pump-turbine model because in turbo-machinery, cavitation can reduce the performance and shorten service life. The pump-turbine model system consists of 7 blades, 20 stay vanes (including tongue) and 20 guide vanes. This study adopts the Rayleigh-Plesset model as a cavitation model, which illustrates cavitation by using the air volume fraction method. The pump mode and turbine mode at the operating condition of partial loading, normal and excessive loading are analyzed to investigate the cavitation performance of the pump-turbine. It was observed that this pump-turbine design showed very good cavitation characteristics with no cavitation bubbles in all operating conditions. Overall value of air volume fraction of both mode at different operating condition are lower than 1, which confirms low possibility of cavitation occurrence at current situation.

• Computers and Concrete
• /
• 제7권5호
• /
• pp.421-435
• /
• 2010

This paper utilizes the modified Davis model and the mode coupling theory, as parts of the electrolyte solution theory, to investigate the diffusivity of the ion in concrete. Firstly, a computational model of the ion diffusion coefficient, which is associated with ion species, pore solution concentration, concrete mix parameters including water-cement ratio and cement volume fraction, and microstructure parameters such as the porosity and tortuosity, is proposed in the saturated concrete. Secondly, the experiments, on which the chloride diffusion coefficient is measured by the rapid chloride penetration test, have been carried out to investigate the validity of the proposed model. The results indicate that the chloride diffusion coefficient obtained by the proposed model is in agreement with the experimental result. Finally, numerical simulation has been completed to investigate the effects of the porosity, tortuosity, water-cement ratio, cement volume fraction and ion concentration in the pore solution on the ion diffusion coefficients. The results show that the ion diffusion coefficient in concrete increases with the porosity, water-cement ratio and cement volume fraction, while we see a decrease with the increasing of tortuosity. Meanwhile, the ion concentration produces more obvious effects on the diffusivity itself, but has almost no effects on the other ions.

• Smart Structures and Systems
• /
• 제26권2호
• /
• pp.253-262
• /
• 2020

In this paper, a new higher order shear deformation model is developed for static analysis of functionally graded beams with considering porosities that may possibly occur inside the functionally graded materials (FGMs) during their fabrication. The model account for higher-order variation of transverse shear strain through the depth of the beam and satisfies the zero traction boundary conditions on the surfaces of the beam without using shear correction factors. The present work aims to study the effect of the distribution forms of porosity on the bending of simply supported FG beam. Based on the present higher-order shear deformation model, the equations of motion are derived by the principle of virtual works. Navier type solution method was used to obtain displacement and stresses, and the numerical results are compared with those available in the literature. A comprehensive parametric study is carried out to assess the effects of volume fraction index, porosity fraction index, and geometry on the bending of imperfect FG beams. It can be concluded that the proposed model is simple and precise for the resolution of the behavior of flexural FGM beams while taking into account the shape of distribution of the porosity.