• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.10a
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• pp.130-133
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• 2008

The formability of DP steels can be affected by not only initial texture but also deformation texture evolved during plastic deformation. To investigate the evolution of deformation texture during deep drawing, deep drawing process for DP steels was carried out experimentally. A rate sensitive polycrystal model was used to predict texture evolution during deep drawing process. In order to evaluate the strain path during deep drawing, a steady state was assumed in the flange part of deep drawn cup. A rate sensitive polycrystal model successfully predicted the texture development in DP steels during deep drawing process. It was found that the final stable orientations were strongly dependent on the initial location in the blank.

• Journal of the Korean Chemical Society
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• v.18 no.3
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• pp.153-156
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• 1974

The kinetics of gas evolution in the reaction between hydrazine and iodine in a sulfuric acid medium has been studied at $25^{\circ}$. The rate is first order in hydrazine and iodine concentration. The iodide ion retards the reaction whereas the effect of hydrogen ion concentration is rather complicated. The rate of gas evolution is very close to that of iodine consumption.

• Publications of The Korean Astronomical Society
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• v.8 no.1
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• pp.179-183
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• 1993

We analyze the evolution of active galactic nuclei for the decreasing accretion rate case. Our analysis is based on the unified theory of active galactic nuclei which entirely depends on the accretion rates of the central supermassive black holes. Our discussion leads us to conclude that active galactic nuclei may evolve from QSOs into the nuclei of Seyfert or radio galaxies.

• Publications of The Korean Astronomical Society
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• v.30 no.2
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• pp.511-512
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• 2015

Star formation activities dominate the evolution of galaxies. Elliptical galaxies are believed to be old galaxies in the Hubble sequence, and elliptical galaxies at different evolution epochs might have different star formation activities and/or morphologies. We investigate the connection between star formation rates and the morphology of elliptical galaxies. With the Sloan Digital Sky Survey (SDSS) and the Galaxy Zoo, we select a sample of elliptical galaxies by morphology and consider their infrared emission as an index of star formation rate to study the relation between the star formation rates and their morphological properties, such as ellipticities. In addition, we select some nearby spiral galaxies with very low MIR emission to probe the mechanisms of these red spiral galaxies. We display our preliminary results and discuss their implication on the evolution of galaxies in this poster.

• Proceedings of the Korean Institute of Intelligent Systems Conference
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• 1998.10a
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• pp.420-426
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• 1998

Evolutionary algorithms are probabilistic optimization algorithms based on the model of natural evolution. Recently the efforts to improve the performance of evolutionary algorithms have been made extensively. In this paper, we introduce the research for improving the convergence rate and search faculty of evolution algorithms by using reinforcement learning. After providing an introduction to evolution algorithms and reinforcement learning, we present adaptive genetic algorithms, reinforcement genetic programming, and reinforcement evolution strategies which are combined with reinforcement learning. Adaptive genetic algorithms generate mutation probabilities of each locus by interacting with the environment according to reinforcement learning. Reinforcement genetic programming executes crossover and mutation operations based on reinforcement and inhibition mechanism of reinforcement learning. Reinforcement evolution strategies use the variances of fitness occurred by mutation to make the reinforcement signals which estimate and control the step length.

• Journal of the Korean Society for Precision Engineering
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• v.14 no.9
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• pp.90-100
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• 1997

A full three-dimensional thermo-coupled rigid-viscoplastic finite element method and the currently developed microstructural evolution system which includes semi-empirical equations suggested by different research groups were used together to form an integrated system of process and micro- structure simulation of hot rolling. The distribution and time histroy of the momechanical variables such as temperature, strain, strain rate, and time during pass and between passes were obtained from the finite element analysis of multipass hot rolling processes. The distribution of metallurgical variables were calculated on the basis of instantaneous thermomechanical data. For the verification of this method the evolution of microstructure in plate rolling and shape rolling was simulated and their results were compared with the data available in the literature. Consequently, this approach makes it possible to describe the realistic evolution of microstructure by avoiding the use of erroneous average value and can be used in CAE of multipass hot rolling.

• Applied Chemistry for Engineering
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• v.9 no.1
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• pp.52-57
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• 1998

The effects of additives such as zinc compounds in 4M KOH electrolyte of Al-air cell have been studied. Zinc compounds in electrolyte increased hydrogen evolution overpotential and TPC(tripotasium citrate)/CaO formed fine film on aluminum surface, and these additives decreased hydrogen evolution rate and corrosion rate of aluminum. These additives shifted the OCP in the positive direction on high purity aluminum(purity, 99.999%) and in the negative direction on Al No 1050(purity,99.5%). Addition of two or more additives resulted in the prevention or the reduction of corrosion rate and hydrogen evolution at OCP. As the overpotential on Al electrode increased, the hydrogen evolution rate decreased and the utilization of aluminum increased. At high current density$(>100mA/cm^2)$, TPC/CaO/ZnO additives increased the utilization of high purity aluminum up to that of aluminum alloys containing indium, gallium and thallium.

• Microbiology and Biotechnology Letters
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• v.27 no.1
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• pp.46-53
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• 1999

The purpose of this study was to optimize the conditions of continuous mixed culture of C.butyricum and R. spaeroides K-7, which were able to produce hydrogen using biomass-dreived substrate. To investigate the possibility of continuous culture, semi-continuous culture was carried out for 20 days. In semi-continuous culture using the reactor system, the replacement rate of fresh medium was 30% of total medium volume for the highest hydrogen evolution. In continuous culture, the optimum dilution rate was determined to be 0.05$h^{-1}$. The continuous culture produced 3.1 times as compared with the hydrogen on batch culture. On the other hand, the continuous mixed culture produced 1.3~2.1 times as much as hydrogen of the continuous monoculture of C. butyricum. When 10g of glucose in the media (1l) was supplied as a carbon source on continuous culture, mixed culture of C. butyricum and R. sphaeroides K-7 increased hydrogen evolution rate. Because considerable amount of glutamate was contained in waste water of glutamate fermentation, utilization of glutamate was examined in mixed culture. As a result of examination, production of hydorgen was slightly inhibited by high concentration of glutamate, more than 20mM, on continuous monoculture of R. sphaeroides K-7. On the other hand, both on continuous monoculture of C. butyricum and on mixed culture of C. butyricum and R. sphaeroides K-7, production of hydrogen was not inhibited by high concentration of glutamate such as 100mM. Hence this suggests that high concentration of waste water can be used as good substrate for hydrogen production on monoculture of C. butyricum and mixed culture of C. butyricum and R. sphaeroides K-7.

• Journal of The Korean Astronomical Society
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• v.29 no.1
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• pp.63-73
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• 1996

The previous study of chemical evolution of the Galaxy is extended to the radial properties of the Galactic disk. The present model includes radial dependency of the time-dependent bimodal IMF, radial flow of material in the disk, and the change of type I supernova explosion rate with radial distance from the disk center as model parameters and observed gas and stellar density distributions and metallicity abundance gradient as observational constraints. The results of two models in this study explain the observed gas and stellar density distributions well, with the slope of the gas density gradient in the region of 4.5 kpc$Y_1$ and -0.123dex/kpc in model $Y_2$, respectively, which fit well the observed gradient of -0.l1dex/kpc. The abundance gradient reproduced in model $Y_1$ is getting flatter with decreasing radius, while that in model $Y_2$ is getting steeper, which fits better the observed abundance gradient. This result shows the necessity of exponentially increasing type I supernova explosion rate with decreasing radius in order to explain the observed abundance gradient in the disk. The fitness of observed density distribution and star formation rate distribution justifies the reliability of time-dependent bimodal IMF as a compound quantitative chemical evolution model of the Galaxy. The temporal variations of metallicity gradients for carbon, nitrogen and oxygen are also shown.

• Korean Chemical Engineering Research
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• v.61 no.4
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• pp.627-634
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• 2023

Graphitic carbon nitride (g-C₃N₄) has attracted considerable attention since its discovery for its catalysis of water splitting to hydrogen and oxygen under visible light irradiation. However, pristine g-C₃N₄ confers only low photocatalytic efficiency and requires surface cocatalysts to reach moderate activity due to a lack of accessible surface active sites. Inspired by the high specific surface area and superior electron transfer of graphene, we developed a strongly coupled binary structure of graphene and g-C₃N₄ aerogel with 3D porous skeleton. The as-prepared 3D structure photocatalysts achieve a high surface area that favors efficient photogenerated charge separation and transfer, enhances the light-harvesting efficiency, and significantly improves the photocatalytic hydrogen evolution rate as well. The photocatalyst performance is observed to be optimized at the ratio 3:7 (g-C₃N₄:GO), leading to photocatalytic H₂ evolution of 16125.1 mmol. g^-1. h^-1 under visible light irradiation, more than 161 times higher than the rate achieved by bulk g-C₃N₄.