• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1997.03a
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• pp.73-76
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• 1997

Nanocrystalline materials have been modeled as a mixture of the crystallite and the grain boundary phases. The mechanical property has been calculated using the rule of mixtures based on the volume fractions. The critical grain size concept suggested by Nieh and Wadsworth and porous material model suggested by Lee and Kim were applied to the calculation. The theoretical results fit very well with the experimental values

• Proceedings of the KIEE Conference
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• 2006.07b
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• pp.677-678
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• 2006

Pressure risc is an important design factor and affects significantly on the characteristics of gas circuit breakers. For self-blast circuit breakers, the nozzle ablation plays important role in pressure-building up and should be properly considered for the accurate calculation. In this paper, the nozzle ablation is treated as a boundary condition and the pressure is calculated from mass fractions of PTFE and SF6. The amount of the ablated mass of a nozzle is assumed to be proportional to the are energy and the area of nozzle surface that directly touches arc. The calculation result is compared with measured data and shows good agreement with it.

• Journal of Elementary Mathematics Education in Korea
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• v.13 no.2
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• pp.285-304
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• 2009

The operations of fractions are the main contents of number and operations in the elementary mathematics curriculum. They are also difficult for students to understand conceptually. Nevertheless, there has been little study on the addition and subtraction of fractions. Given this, this paper explored the connection between the national mathematics curriculum and its concomitant textbooks, the adequacy of when to teach, and the method of constructing each unit to teach addition and subtraction of fractions. This paper then analyzed elementary mathematics textbooks and workbooks by three parts aligned with the general instructional flow: 'introduction', 'activity', and, 'exercise'. First, it was analyzed with regard to the introduction part whether the word problems of textbooks might reflect on students' daily lives as intended, how different meanings of operations would be expected to be taught, and how the subsequent activities were connected with the original word problems. Second, the main analysis of activity part of the textbooks dealt with how to use concrete or iconic models to promote students' conceptual understanding of operations and how to formalize the calculation methods and principles with regard to addition and subtraction of fractions. Third, the analysis of the part of exercise in the textbooks and workbooks was conducted with regard to problem types and meanings of operations. It is expected that the issues and suggestions stemming from this analysis of current textbooks and workbooks are informative in developing new instructional materials aligned to the recently revised mathematics curriculum.

• Journal of Elementary Mathematics Education in Korea
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• v.15 no.1
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• pp.1-18
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• 2011

The purpose of this study was to investigate the effects of estimation strategy on placing decimal point in multiplication and division of decimals. To examine the effects of improving calculation ability and reducing decimal point errors with this estimation strategy, the experimental research on operation with decimal was conducted. The operation group conducted the decimal point estimation strategy for operating decimal fractions, whereas the control group used the traditional method with the same test paper. The results obtained in this research are as follows; First, the estimation strategy with understanding a basic meaning of decimals was much more effective in calculation improvement than the algorithm study with repeated calculations. Second, the mathematical problem solving ability - including the whole procedure for solving the mathematical question - had no effects since the decimal point estimation strategy is normally performed after finishing problem solving strategy. Third, the estimation strategy showed positive effects on the calculation ability. Th Memorizing algorithm doesn't last long to the students, but the estimation strategy based on the concept and the position of decimal fraction affects continually to the students. Finally, the estimation strategy assisted the students in understanding the connection of the position of decimal points in the product with that in the multiplicand or the multiplier. Moreover, this strategy suggested to the students that there was relation between the placing decimal point of the quotient and that of the dividend.

• Nuclear Engineering and Technology
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• v.55 no.1
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• pp.109-118
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• 2023

In this paper, the evaluation method of fluidelastic instability (FEI) of newly designed steam generator tubing in pressurized water reactor (PWR) nuclear power plants is discussed. To obtain the parameters for prediction of the critical velocity of FEI for steam generator tubes, experimental research is carried out, and the design parameters are determined. Using CFD numerical simulation, the tube array scale of the model experiment is determined, and the experimental device is designed. In this paper, 7 groups of experiments with void fractions of 0% (water), 10%, 20%, 50%, 75%, 85% and 95% were carried out. The critical damping ration, fundamental frequency and critical velocity of FEI of tubes in flowing water were measured. Through calculation, the total mass and instability constant of the immersed tube are obtained. The critical damping ration measured in the experiment mainly included two-phase damping and viscous damping, which changed with the change in void fraction from 1.56% to 4.34%. This value can be used in the steam generator design described in this paper and is conservative. By introducing the multiplier of frequency and square root of total mass per unit length, it is found that the difference between the experimental results and the calculated results is less than 1%, which proves the rationality and feasibility of the calculation method of frequency and total mass per unit length in engineering design. Through calculation, the instability constant is greater than 4 when the void fraction is less than 75%, less than 4 when the void fraction exceeds 75% and only 3.04 when the void fraction is 95%.

• Journal of Mechanical Science and Technology
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• v.20 no.6
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• pp.748-758
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• 2006

In this paper, we have revisited the estimation of the rotational stiffness of sidewall of radial tire and have suggested a new method for evaluation of the rotational stiffness. Since thicknesses, and volume fractions of the constituents of sidewall are varied depending on radial position, the equivalent shear modulus of the sidewall also depends on radial position. For the estimation of rotational stiffness of sidewall's rubber, we have divided its cross-section into sufficient numbers of small parts and have calculated the equivalent shear modulus of each part of sidewall. Using the shear moduli of divided parts, we have obtained the rotational stiffness by employing in-plane shear deformation theory. This method is expected to be a useful tool in tire design since it relates such basic variables to the global stillness of tire. Applying the calculation method to a radial tire of P205/60R15, we have compared its rotational stiffness with experimental one.

• Journal of Korean Vacuum Science & Technology
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• v.3 no.2
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• pp.116-120
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• 1999

Possible role of hydrogen atoms on the formation of microcrystalline silicon films was schematically investigated using a plasma enhanced chemical vapor deposition system. A layer-by-layer technique that can alternate deposition of ${\alpha}$-Si thin film and then exposure of H2 plasma was used for this end. The experimental process was extensively carried out under different hydrogen plasma times (t2) at a fixed number of 20 cycles in the deposition. structural properties, such as crystalline volume fractions and grain shapes were analyzed by using a Raman spectroscopy and a scanning electron microscopy. Electrical transports were characterized by the temperature dependence of the dark conductivity that gives rise to the calculation of activation energy (Ea). Optical absorption was measured using an ultra violet spectrophotometer, resulting in the optical energy gap (Eopt). Our experimental results indicate that both of the hydrogen etching and the structural relaxation effects on the film surface seem to be responsible for the growth mechanism of the crystallites in the ${\mu}$c-si films.

• Nuclear Engineering and Technology
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• v.51 no.6
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• pp.1650-1657
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• 2019

Fluidelastic instability and nonlinear dynamics of tube bundles is a key issue in a steam generator. Especially, once the post-instability motion of the tube becomes larger than the clearance gap to other tubes, effective contact or impact between the tubes under consideration and the other tube inevitable. There is seldom theoretical analysis to the nonlinear dynamic characteristics of a tube array in two-phase flow. In this paper, experimental and numerical studies were utilized to obtain the critical velocity of the flow-induced instability of a rotated triangular tube array. The calculation results agreed well with the experimental data. To explore the post-instability dynamics of the tube array system, a Runge-Kutta scheme was used to solve the nonlinear governing equations of tube motion. The numerical results indicated that, when the flow pitch velocity is larger than the critical velocity, the tube array system is undergoing a limit cycle motion, and the dynamic characteristics of the tube array are almost similar for different void fractions.

• Nuclear Engineering and Technology
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• v.54 no.7
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• pp.2690-2701
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• 2022

In this paper, we select important fission products for the estimation of the source term during a severe accident of a PWR. The selection is based on the numerical results obtained from depletion calculations for the typical PWR fuel via the in-house code named DEGETION (Depletion, Generation, and Transmutation of Isotopes on Nuclear Application), release fractions of the fission products derived from NUREG-1465, and effective dose conversion coefficients from ICRP 119. Then, for the selected fission products, we obtain the adjoint solutions of the Bateman equations for radioactive decay in order to determine the importance of precursors producing the aforementioned fission products via radioactive decay, which would provide insights into the assumption used in MACCS 2 for a level 3 PSA analysis in which up to six precursors are considered in the calculations of radioactive decays for the fission product after release from the reactor.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.1
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• pp.25-31
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• 2001

The theoretical modeling to predict the modulus of elasticity by the shape memory effect of dispersed particles in a metal matrix composite was studied. The modeling approach is based on the Eshelbys equivalent inclusion method and Mori-Tanakas mean field theory. The calculation was performed on the TiNi particle dispersed Al metal matrix composites(PDMMC) with varying volume fractions and prestrains of the particle. It was found that the prestrain has no effect on the Yonugs modulus of PDMMC but the volume fraction does affects it. This approach has an advantage of definite control of Youngs modulus in PDMMCs.