• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2005년도 춘계학술대회 논문집
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• pp.1812-1818
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• 2005

Even though SMA actuators have high power to volume ratio, there exist disadvantages such as hysteresis and saturation. So the model identification for SMA actuators is very difficult. For the qualitative model identification, we described the behavior of SMA actuators using a so-called diagonal model, which can readily expect the turning point of an incomplete phase transformation. For the quantitative model identification, we developed the general dynamics of SMA actuators using the modified Liang's model. Using this dynamics we can describe the hysteresis and the saturation very well. It is also very important to notice that the modified Liang's model maintains a continuous martensite fraction at the change of the phase transformation but the original model cannot.

• 한국학교수학회논문집
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• 제12권2호
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• pp.151-170
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• 2009

초등학생에게 분수는 추상적인 개념이며 형식화된 이해를 요구하는, 핵심적인 수학적 기초 내용이다. 초등학교 수학에서 중학교 수학으로 연계되는 내용의 위계 구조상 적지 않은 영향력을 끼치는 내용 중 하나가 초등수학에서의 분수 학습일 것이다. 이에 본 연구에서는 초등학교 6학년생에게 나타난 분수 개념에 대한 이해와 오류를 분석하고 초등학교 학생이 가장 어려워하는 분수 나눗셈에 대한 표현 능력을 살펴봄으로써 초등수학에서의 시사점을 제공하고자 한다.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2007년도 제34회 KOSCO SYMPOSIUM 논문집
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• pp.118-125
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• 2007

The firtst-order conditional moment closure (CMC) model is applied to CH4/air swirl diffusion flame in a gas turbine model combustor. The flow and mixing fields are calculated by fast chemistry assumption with SLFM library and a beta function pdf for mixture fraction. RNG k-e model is used to consider the swirl flame in a confined wall. Reacting scalar fields are calculated by elliptic CMC formulation with chemical kinetic mechanism, GRI Mech 3.0. Validation is done against measurement data for mean flow and scalar fields in the model combustor [1]. Results show reasonable agreement with the mean mixture fraction and its variance, while temperature is overpredicted as the level of local extinction increases. The second-order CMC model is needed to consider local extinction with considerable conditional fluctuations near the nozzle.

• 한국학교수학회논문집
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• 제25권4호
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• pp.307-332
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• 2022

본 연구는 수학교실에서 지속적으로 활용할 수 있는 반구체물 분수교구를 제작·활용함으로써 학생들의 분수학습을 돕기 위한 목적으로 실행되었다. 이를 위해서 학생들과 직접 분수교구를 제작하였고, 4차시에 걸쳐 이전의 분수내용의 복습에 분수교구를 활용함으로써 본 학습 전에 분수교구의 활용방법을 익혔다. 이후 원리 탐구 학습 모형을 적용한 14차시의 수업을 통해 약분과 통분(7차시), 이분모 분수의 덧셈과 뺄셈(7차시) 학습에 분수교구를 활용하여 원리를 탐구하도록 하였다. 학생들은 분수교구를 활용하여 다양한 분수를 나타낼 수 있었고 이를 이용해서 분수연산문제를 해결할 수 있었다. 수업 후 성취도평가를 통해서 학생들이 반구체물교구-표상-수식을 연결시킬 수 있음을 알 수 있었고, 분수교구를 활용한 수업을 통해 수학에 대한 흥미와 자신감을 보임을 알 수 있었다.

• 한국연소학회지
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• 제15권4호
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• pp.15-21
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• 2010

The transported probability density function(PDF) model has been applied to simulate the turbulent nonpremixed piloted jet flame. To realistically account for the mixture fraction PDF informations on the turbulent non-premixed jet flame, the present Lagrangian PDF transport approach is based on the joint velocity-composition-turbulence frequency PDF formulation. The fluctuating velocity of stochastic fields is modeled by simplified Langevin model(SLM), turbulence frequency of stochastic fields is modeled by Jayesh-Pope model and effects of molecular diffusion are represented by the interaction by exchange with the mean (IEM) mixing model. To validate the present approach, the numerical results obtained by the joint velocity-composition-turbulence frequency PDF model are compared with experimental data in terms of the unconditional and conditional means of mixture fraction, temperature and species and PDFs.

• 약학회지
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• 제47권5호
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• pp.307-310
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• 2003

Ethanol extract of Actinidia polygama Max. (AP) was examined for hypouricemic activity in potassium oxonateinduced hyperuricemic animal model. Ethanol extract of AP lowered the plasma uric acid level by 20％ when compared to the hyperuricemic control group. AP ether fraction at a dose of 100 mg/kg showed 27％ reduction, whose efficacy was comparable to the probenecid-treated group. AP ether fraction-treated group also showed 23％ reduction of urate in urine and this result suggests that AP ether fraction has anti-gout activity probably due to xanthine oxidase inhibition.

• Computers and Concrete
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• 제8권2호
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• pp.163-176
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• 2011

By virtue of chord-length density function from the field of statistical physics, this paper introduced a quantitative approach to estimate the distribution of cement paste thickness between aggregates in concrete. Dynamics mixing method based on molecular dynamics was employed to generate one model structure, then image analysis algorithm was used to obtain the distribution of thickness of cement paste in model structure for the purpose of verification. By comparison of probability density curves and cumulative probability curves of the cement paste thickness among neighboring aggregates, it is found that the theoretical results are consistent with the simulation. Furthermore, for the model mortar and concrete mixtures with practical volume fraction of Fuller-type aggregate, this analytical formula was employed to predict the influence of aggregate volume fraction and aggregate fineness. And evolution of its mean values were also investigated with the variation of volume fraction of aggregate as well as the fineness of aggregates in model mortars and concretes.

• Computers and Concrete
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• 제25권4호
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• pp.303-310
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• 2020

In this research, a hybrid mathematical model is derived using the higher-order polynomial kinematic model in association with soft computing technique for the prediction of best fiber volume fractions and the minimal mass of the layered composite structure. The optimal values are predicted further by taking the frequency parameter as the constraint and the projected values utilized for the computation of the eigenvalue and deflections. The optimal mass of the total layered composite and the corresponding optimal volume fractions are evaluated using the particle swarm optimization by constraining the arbitrary frequency value as mass/volume minimization functions. The degree of accuracy of the optimal model has been proven through the comparison study with published well-known research data. Further, the predicted values of volume fractions are incurred for the evaluation of the eigenvalue and the deflection data of the composite structure. To obtain the structural responses i.e. vibrational frequency and the central deflections the proposed higher-order polynomial FE model adopted. Finally, a series of numerical experimentations are carried out using the optimal fibre volume fraction for the prediction of the optimal frequencies and deflections including associated structural parameter.

• 열처리공학회지
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• 제37권3호
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• pp.103-113
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• 2024

Martensite volume fraction significantly affects the mechanical properties of alloy steels. Martensite start temperature (M_s), transformation temperature for martensite 50 vol.% (M₅₀), and transformation temperature for martensite 90 vol.% (M₉₀) are important transformation temperatures to control the martensite phase fraction. Several researchers proposed empirical equations and machine learning models to predict the Ms temperature. These numerical approaches can easily predict the Ms temperature without additional experiment and cost. However, to control martensite phase fraction more precisely, we need to reduce prediction error of the Ms model and propose prediction models for other martensite transformation temperatures (M₅₀, M₉₀). In the present study, machine learning model was applied to suggest the predictive model for the Ms, M50, M90 temperatures. To explain prediction mechanisms and suggest feature importance on martensite transformation temperature of machine learning models, the explainable artificial intelligence (XAI) is employed. Random forest regression (RFR) showed the best performance for predicting the Ms, M50, M90 temperatures using different machine learning models. The feature importance was proposed and the prediction mechanisms were discussed by XAI.

• 생약학회지
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• 제40권1호
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• pp.51-58
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• 2009

The anti-hyperlipidemic effects of an ethyl acetate fraction from Orostachy japonicus in a high lipid diet-induced hyperlipidemic rat model were assessed. The fraction, which contained kaempferol, astragalin, and isoquercitrin, was associated with significant weight loss and reduction of lipid contents in serum and liver tissues. The fraction, which contains mainly flavonoids, diminished the levels of malondialdehyde and hydroxyl radical, and increased the anti-oxidative enzyme activities of superoxide dismutase, catalase, and glutathione peroxidase. Reduced bleeding and plasma clotting times resulting from the administration of the ethyl acetate fraction may reduce cardiovascular disease associated with hyperlipidemia.