• 대한전기학회:학술대회논문집
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• 대한전기학회 2008년도 학술대회 논문집 정보 및 제어부문
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• pp.165-168
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• 2008

The experimental results of exposing IGBT (Insulated Gate Bipolar Transistor) samples to gamma radiation source show shifting of threshold voltages in the MOSFET and degradation of carrier mobility and current gains. At low total dose rate, the shift of threshold voltage is the major contribution of current increases, but for more than some total dose, the current is increased because of the current gain degradation occurred in the vertical PNP at the output of the IGBTs. In the paper, the collector current characteristics as a function of gate emitter voltage (VGE) curves are tested and analyzed with the model considering the radiation damage on the devices for gate bias and different dose. In addition, the model parameters between simulations and experiments are found and studied.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2006년도 춘계학술대회 논문집
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• pp.429-433
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• 2006

High Temperature deformation behavior of newly developed beta-gamma TiAl alloy was investigated in this study. The optimum processing condition was investigated with the aid of Dynamic Materials Model (DMM). Processing maps representing the efficiency of power dissipation for microstructural evolution and instability were constructed utilizing the results of hot compression test at temperatures ranging from $1000^{\circ}C$ to $1200^{\circ}C$ and strain rate ranging from $10^{-4}/s$ to $10^2/s$. The Artificial Neural Network (ANN) simulation was adopted to consider the deformation heating. With the help of processing map and microstructural analysis, the optimum processing condition was presented and the role of $\beta$ phase was also discussed in this study.

• 천문학회보
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• 제35권1호
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• pp.83.2-83.2
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• 2010

During the formation of cosmic web, collisionless shock waves are produced around and inside the substructures. In these shock waves electrons and ions are accelerated to such high energies that they can produce gamma rays in several ways. Many authors have studied the contribution of shock-induced radiation to the cosmic gamma-ray background. However not all the important physical processes are included in their calculation. By considering more complete physical process, we re-investigate the problem. In our model, the energy distribution of the cosmic rays (CRs) are calculated by widely accepted diffusive shock acceleration model, both primary and secondary CR electrons are included, both inverse Compton scattering and bremsstrahlung process are considered. The difference of the results are discussed.

• Communications for Statistical Applications and Methods
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• 제24권2호
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• pp.129-142
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• 2017

In this paper we consider the problem of the model selection/discrimination among three different positively skewed lifetime distributions. Lindley, Weibull, and gamma distributions have been used to effectively analyze positively skewed lifetime data. This paper assesses how much closer the Lindley distribution gets to Weibull and gamma distributions. We consider three techniques that involve the likelihood ratio test, asymptotic likelihood ratio test, and minimum Kolmogorov distance as optimality criteria to diagnose the appropriate fitting model among the three distributions for a given data set. Monte Carlo simulation study is performed for computing the probability of correct selection based on the considered optimality criteria among these families of distributions for various choices of sample sizes and shape parameters. It is observed that overall, the Lindley distribution is closer to Weibull distribution in the sense of likelihood ratio and Kolmogorov criteria. A real data set is presented and analyzed for illustrative purposes.

• Archives of Pharmacal Research
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• 제29권8호
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• pp.685-690
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• 2006

The effect of a main constituent ginsenoside Rg5 isolated from red ginseng and its metabolite ginsenoside Rh3 in a chronic dermatitis model was investigated. Ginsenosides Rg5 and Rh3 suppressed swelling of oxazolone-induced mouse ear contact dermatitis. These ginsenosides also reduced mRNA expressions of cyclooxygenase-2, interleukin $(IL)-1{\beta}$, tumor necrosis factor $(TNF)-{\alpha}$ and interferon $(IFN)-{\gamma}$. The inhibition of ginsenoside Rh3 was more potent than that of ginsenoside Rg5. These findings suggest that ginsenoside Rh3 metabolized from ginsenoside Rg5 may improve chronic dermatitis or psoriasis by the regulation of $IL-1{\beta}$ and $TNF-{\alpha}$ produced by macrophage cells and of $IFN-{\gamma}$ produced by Th cells.

• Nuclear Engineering and Technology
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• 제34권1호
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• pp.22-29
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• 2002

The angular correlation effect was investigated for Co-60 ${\gamma}$-ray spectroscopy by using HPGe detector and the effective angular correlation was theoretically calculated by considering the finite detector solid angle. For the calculation of effective angular correlation, the detection efficiency as a function of ${\gamma}$-ray incident direction was obtained by using Monte Carlo method and the first interaction model. The results and the methods used in the calculation are discussed.

• 대한금속재료학회지
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• 제49권2호
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• pp.137-144
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• 2011

Strengthening mechanisms in an ordered intermetallic compound containing coherent precipitates of lower antiphase boundary energy than the matrix were investigated on the basis of the interaction between the deformation induced dislocations and the disordered precipitates in an $Ll_2$ ordered $Ni_3Al$-based alloy. Extra work was needed to pull out the dislocations from the precipitate, which was dependent on the difference in the antiphase boundary energy between the matrix and the precipitate, as well as the size and volume fraction of the precipitate. The strength of the $Ll_2$ ordered ${\gamma}^{\prime}$ phase containing fine precipitates of the disordered ${\gamma}$ phase was examined using the proposed model. The model can explain almost quantitatively the age hardening behavior of the $Ll_2$ ordered ${\gamma}^{\prime}$ phase.

• Animal Systematics, Evolution and Diversity
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• 제30권1호
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• pp.39-43
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• 2014

In this brief report, alternative time-varying diversification rate models were fitted onto the phylogeny of global amphibians by considering one-constant-rate (OCR), one-continuous-shift (OCS) and multiple-discrete- shifts (MDS) situations. The OCS diversification model was rejected by ${\gamma}$ statistic (${\gamma}=-5.556$, p<0.001), implying the existence of shifting diversification rates for global amphibian phylogeny. Through model selection, MDS diversification model outperformed OCS and OCR models using "laser" package under R environment. Moreover, MDS models, implemented using another R package "MEDUSA", indicated that there were sixteen shifts over the internal nodes for amphibian phylogeny. Conclusively, both OCS and MDS models are recommended to compare so as to better quantify rate-shifting trends of species diversification. MDS diversification models should be preferential for large phylogenies using "MEDUSA" package in which any arbitrary numbers of shifts are allowed to model.

• 대한기계학회논문집B
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• 제33권12호
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• pp.1014-1021
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• 2009

A new eddy viscosity equation was formulated from assumption of turbulence length scale equation and specific dissipation ratio equation. Then, a set of turbulence model equations for the turbulent kinetic energy ${\kappa}$, the viscosity ${\nu}_t$, and the intermittency factor ${\gamma}$ is proposed by considering the entrainment effect. Closure coefficients are determined by experimental data and resorting to numerical optimization. Present model has been applied to compute four representative cases of free shear flows and successfully compared with experimental data. In particular, the spreading rate, the centreline mean velocity and the profiles of intermittency are calculated with improved accuracy. Also, the proposed ${\nu}_t-{\kappa}-{\gamma}$ model was applied to channel flow by considering the wall effect and the results show good agreements with the Direct Numerical Simulation data.

• 한국조경학회지
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• 제38권5_2호
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• pp.151-162
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• 2010

This research aimed at measuring Park and Green Satisfaction (PGS) using subjective indicators of 'surface, line and spot' green evaluated by citizens. Also frequency of visits to park and green measured using objective indicators (number of visits) to find the relationship with PGS. A conceptual model of PGS was developed to relate evaluation to satisfaction and finally to utilization of open spaces. A sample of 500 questionnaire survey was employed for Uijeongbu City in Korea. A Structual Equation Modeling (AMOS) techniques was used to test the hypothesized relationship among factors (construct). As a result, first, PGS was explained by three latent factors of 'urban park' (${\gamma}=0.54$), 'linear facilities' (${\gamma}=0.25$), and 'surface green' (${\gamma}=0.15$) respectively. These three exogenous construct was found very useful classification system for open spaces of cities. Second, PGS (${\gamma}=0.34$) was found as a mediating variable to utilization of open spaces and also PGS was closely related to citizens Environmental Quality Satisfaction (EQS), such concept as, 'livability' and 'aesthetic quality'. The more satisfied with park and green the more people use the space. The PGS was an important QOL indicator together with the subjective indicator of 'livability'. Third, jogging and walking trails and bike ways along the river corridor was the most important green facilities contribute to the PGS and EQS. The near the distance (within 500m) the more number of visit to river corridor (green way). The river corridor promote accessibility to nature and other parks.