• Structural Engineering and Mechanics
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• 제66권5호
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• pp.649-663
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• 2018

The scaled boundary finite element method is extended to evaluate the dynamic stress intensity factors and T-stress with a numerical procedure based on the improved continued-fraction. The improved continued-fraction approach for the dynamic stiffness matrix is introduced to represent the inertial effect at high frequencies, which leads to numerically better conditioned matrices. After separating the singular stress term from other high order terms, the internal displacements can be obtained by numerical integration and no mesh refinement is needed around the crack tip. The condition numbers of coefficient matrix of the improved method are much smaller than that of the original method, which shows that the improved algorithm can obtain well-conditioned coefficient matrices, and the efficiency of the solution process and its stability can be significantly improved. Several numerical examples are presented to demonstrate the increased robustness and efficiency of the proposed method in both homogeneous and bimaterial crack problems.

• 한국세라믹학회지
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• 제38권12호
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• pp.1075-1079
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• 2001

The R-curve for in situ-toughened SiC-30 wt% TiC composites was estimated by the indentation-strength method and compared to that of monolithic SiC with toughened microstructure. Both materials exhibited rising R-curve behavior. The SiC-TiC composites, however, displayed better damage tolerance and higher resistance to crack growth. Total volume fractions of SiC key grains, which take part in toughening mechanisms such as crack bridging and crack deflection, were 0.607 for monolithic SiC ceramics and 0.614 for SiC-TiC composites. From the microstructural characterization and the residual stress calculation, it was inferred that this superior performance of SiC-TiC composites can be attributed to stress-induced microcracking at heterophase (SiC/TiC) boundaries and some contribution from carck deflection by TiC grains.

• 한국연소학회지
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• 제13권3호
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• pp.24-32
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• 2008

Steady Laminar Flamelet Model (SLFM) calculation is performed to compare the turbulent combustion characteristics of air combustion and oxy-combustion with $CO_2$ recirculation. Radiative heat loss is considered by the optically thin limit assumption. For more realistic simulation the first-order conditional moment closure(CMC) model is applied to SANDIA PILOTED FLAME D again for the oxidants of air and mixture of $O_2$ and $CO_2$. The chemical kinetic machanism for methane is GRI Mech 3.0. Results show that oxy flames are much more stable than air flames, while comparable stability is maintained with 65% $CO_2$ recirculation. The comparable peak temperature is maintained with 80% $CO_2$ recirculation. Higher the temperature, higher the fractions of intermediate species, CO and OH, due to dissociation.

• 열처리공학회지
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• 제32권1호
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• pp.17-28
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• 2019

Jominy hardenability curves of low alloy steel containing less than 5 wt.% of alloying elements in total were calculated by applying Scheil's rule of additivity to pre-calculated isothermal transformation curve. Isothermal transformation curve for each phase in steel was approximated as a simple mathematical equation by using Kirkaldy's approach and all coefficients in the equation were estimated from experimental temperature-time-transformation (TTT) and/or continuous cooling transformation (CCT) data in the literature. Then jominy test with simple boundary conditions was performed in computer by applying the finite difference scheme. The resultant cooling curves at each location along a longitudinal direction of Jominy bar were applied to calculate phase fractions as well as mechanical properties such as micro Vickers hardness. The simulated results were compared with experimental CCT data and Jominy curves in the literature.

• 한국자동차공학회논문집
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• 제10권6호
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• pp.11-18
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• 2002

Residual gas fraction in an engine cylinder affects engine performance, efficiency and emission characteristics. With high residual gas fractions, a flame speed and maximum combustion temperature are decreased and these are deeply related with combustion stability especially at idle and NOx emission at relatively high engine load. In this work, the residual gas fraction was calculated by an engine simulation code, which was validated by the experimental data (cylinder pressure and emissions) obtained from 4-cyliner spark ignition engine. A comparison between experimental and computational calculation results was made. The residual gas is generated mostly at low engine speed by the larger pressure difference between the intake and exhaust port. As the valve overlap duration was increased, the amount of residual gas in the cylinder, the amount of HC emission in the exhaust gas and the variation of power output increased.

• 한국수학교육학회지시리즈D:수학교육연구
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• 제22권4호
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• pp.283-304
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• 2019

This paper investigates what informal knowledge and strategies fifth-grade students brought to a classroom and how much they had potential to solve fraction division story problems. The findings show that most of the participants were engaged to understand the meaning of fraction division prior to their formal instruction at school. In order to solve the story problems, the informal knowledge related to fractions as well as division was actively utilized in student's strategies and justification. Students also used various informal strategies from mental calculation, direct modeling, to relational thinking. Formal instructions about fraction division at schools can be facilitated for sense-making of this complex fraction division conception by unpacking informal knowledge and thinking they might bring to the classrooms.

• 보건행정학회지
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• 제10권3호
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• pp.169-187
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• 2000

Cigarette smoking has been identified as the most important source of preventable morbidity and premature mortality (WHO, 1995), The prevalence of smoking among men is very high in Korea. This study estimated productivity losses due to smoking in Korea, 1997. The derivation of cost estimates for mortality, disability, hospitalization and use of physician services related to cigarette smoking is bas 어 on the calculation of attributable fractions suggested by MacMahon and Cole and Smoking-Attributable Mortality, Morbidity, and Economic Cost(SAMMEC) software. To estimate the number of deaths from neoplastic, cardiovascular, respiratory diseases associated with cigarette smoking, estimates for adults(aged 20 years and over) were based on 1997 mortality data, 1995 data on smoking prevalence from Korea Institute for Health and Social Affairs. Smoking-attributable indirect morbidity cost data were obtained from the National Federation of Medical Insurance. As the result of cost estimation, these productivity losses were 336-430 billion won. During 1997, 8,620-10,804 deaths were attributed to smoking. Cigarette smoking resulted in 133,991-169,422 Years of Potential Life Lost (YPLL) to life expectancy. For smoking -attributable indirect mortality costs, the present value of future earnings(PVFE) for the age at death are 299-384 billion won. Smoking-attributable indirect morbidity costs, the costs of lost productivity for persons who are disabled by smoking-related chronic diseases are 37-46 billion won. In this study the productivity losses due to smoking were restricted to the health effects of smoking. It is possible that these costs were underestimated with the limitation of the data. Smoking is the leading preventable cause of illness and death. The results of this study can be used as elementary data for antismoking policy.

• Nuclear Engineering and Technology
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• 제55권11호
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• pp.4287-4294
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• 2023

In order to meet the energy demand, energy production must be done continuously. Hydrogen seems to be the best alternative for this energy production, because it is both an environmentally friendly and renewable energy source. In this study, the hydrogen fuel production of the peaceful nuclear explosives (PACER) fusion blanket as the energy source integrated with Fe-Cl thermochemical water splitting cycle have been investigated. Firstly, neutronic analyzes of the PACER fusion blanket were performed. Necessary neutronic studies were performed in the Monte Carlo calculation method. Molten salt fuel has been considered mole-fractions of heavy metal salt (ThF₄, UF₄ and ThF₄+UF₄) by 2, 6 and 12 mol. % with Flibe as the main constituent. Secondly, potential of the hydrogen fuel production as a result of the neutronic evaluations of the PACER fusion blanket integrated with Fe-Cl thermochemical cycle have been performed. In these calculations, tritium breeding (TBR), energy multiplication factor (M), thermal power ratio (1 - 𝜓), total thermal power (P_hpf) and mass flow rate of hydrogen (ṁ_H2) have been computed. As a results, the amount of the hydrogen production (ṁ_H2) have been obtained in the range of 232.24x10⁶ kg/year and 345.79 x10⁶ kg/year for the all mole-fractions of heavy metal salts using in the blanket.

• 대한수학교육학회지:수학교육학연구
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• 제19권2호
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• pp.307-319
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• 2009

현재 학교수학에서는 자연수로부터 실수에 이르는 덧 뺄셈을 자연수, 분수, 소수, 제곱근 등의 순서로 다루고 있다. 그런데 각 단계에서의 덧 뺄셈 계산 방법을 습득하는데 중점을 둔 나머지, 실수 체계 전반을 아우르는 덧 뺄셈의 통합적 원리에 대한 이해가 부족한 상태에서 학습 지도가 이루어지는 것으로 보인다. 본 연구는 이와 같은 덧 뺄셈의 학습지도가 갖는 한계에 대한 문제의식으로부터 출발한다. 여기서는 수 개념 발생의 심리적 기원을 측정이라고 본 Dewey의 통찰을 확장하여, 덧 뺄셈을 측정활동 내에서 파악하고 이 때 드러나는 공통단위를 기반으로 하면 자연수에서 실수에 이르는 덧 뺄셈 연산의 서로 다른 알고리즘 외양 이면에 공통적인 본질이 있음을 밝힌다. 이러한 논의를 바탕으로 학교수학에서 덧 뺄셈 지도 개선의 필요성을 제시하고자 한다.

• 한국수학교육학회지시리즈C:초등수학교육
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• 제27권1호
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• pp.91-110
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• 2024

본 연구의 목적은 이 통합모델인 직사각형 분할 모델을 초등학교 교실에서 교수·학습하였을 때, 학생들이 이 통합모델을 어떻게 이해하는지, 분수 나눗셈 상황들 사이의 관계를 어떻게 구성하는지 알아보는 데 있다. 이 연구를 통해 얻은 결론은 다음과 같다. 첫째, 제수의 역수를 곱하는 이유나 역수의 의미를 상기시키기 위해서 분수의 나눗셈식을 측정 맥락이나 단위 비율 결정 맥락으로 해석하여 계산 과정을 설명할 필요가 있다. 둘째, 직사각형 분할 모델은 분수의 나눗셈식을 측정 맥락으로 해석할 때 기존 모델에서 나타나는 우회적이거나 부적절한 부분을 보완할 수 있다. 또한 카테시안 곱의 역 맥락의 문제에서 표준알고리즘을 도출하기에 적절한 모델이라고 할 수 있다. 셋째, 카테시안 곱의 역 맥락에서 직사각형 분할 모델은 측정 맥락과 단위 비율 결정 맥락에서의 계산 과정을 자연스럽게 드러낼 수 있다. 그리고 하나의 나눗셈식이 왜 두 가지 해석이 가능한지를 보여줄 수 있어 통합모델로 사용할 수 있다.