• Transactions of the Korean hydrogen and new energy society
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• v.14 no.1
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• pp.1-7
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• 2003

In this study, activity changes of $Ni/Ce-ZrO_2$ catalyst for steam reforming reaction in the various steam treatment condition were investigated and BET, XRD and XPS analysis were introduced to characterize the catalyst before and after treatment. Activity test showed that $Ni/Ce-ZrO_2$ catalyst had good activity after reduction in steam reforming reaction but deactivated rapidly after steam treatment at high temperature. Activities of deactivated catalyst by steam was recovered to die previous activity level after reduction using hydrogen rich gas. It was observed that catalytic activity was preserved after repeated steam treatment, too. It showed that change of catalytic activity due to steam treatment is perfectly reversible. From the BET, XRD and XPS analysis, deactivation of $Ni/Ce-ZrO_2$ catalyst was due to the transition from Ni, that is activity site for steam reforming reaction, to $NiAl_2O_4$ in steam treatment at high temperature.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.17 no.1
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• pp.90-97
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• 1992

An estimation method for the amplitude and phase response of transmission line is discussed. and applied to narrow band ISDN subscriber line. The ABCD parameters of line are evaluated from four impedance values: the standard termination impedence at activated and deactivated stares, and the input impedances of line which can be estimated at each state. Estimating input impedence, the “chirp” signal is used as incident signal and noise effect can be reduced by ensemble averaging. These ABCD parameter estimations might be applicable to ether uniform or nonuniform line. Cleary the magnitude and phase response can be obtained from estimated ABCD parameters. The numerical simulation results for N ISDN subscriber line model are included, and the estimation error introduced by deviation in load impedence is also anlyzed.

• Bulletin of the Korean Chemical Society
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• v.24 no.1
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• pp.86-90
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• 2003

Reverse-Water-Gas-Shift reaction (RWGSR) was carried out over the ZnO, $Al_2O_3,\;and\;ZnO/Al_2O_3$ catalysts at the temperature range from 400 to 700 ℃. The ZnO showed good specific reaction activity but this catalyst was deactivated. All the catalysts except the $ZnO/Al_2O_3$ catalyst (850 ℃) showed low stability for the RWGSR and was deactivated at the reaction temperature of 600 ℃. The $ZnO/Al_2O_3$ catalyst calcined at 850 ℃ was stable during 210 hrs under the reaction conditions of 600 ℃ and 150,000 GHSV, showing CO selectivity of 100% even at the pressure of 5 atm. The high stability of the $ZnO/Al_2O_3$ catalyst (850 ℃) was attributed to the prevention of ZnO reduction by the formation of $ZnAl_2O_4$ spinel structure. The spinel structure of $ZnAl_2O_4$ phase in the $ZnO/Al_2O_3$ catalyst calcined at 850 ℃ was confirmed by XRD and electron diffraction.

• Journal of Korean Society of Environmental Engineers
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• v.34 no.10
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• pp.664-670
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• 2012

A study on the in situ regeneration effect of commercial deactivated SCR catalyst which had been exposed to the off gas from the heavy oil fired power plant for a long time was carried out in a simulated in situ conditions by washing with distilled water and various acid solutions in a short time. The catalytic performance test of the regenerated SCR catalysts was carried out in the micro reactor with simulated off gas of the heavy oil fired power plant and all prepared catalysts were characterized by BET, Porosimeter, EDX (Energy Dispersive X-ray spectrometer) and ICP (Inductively Coupled Plasma) to investigate correlations between catalytic activity and surface characteristics of them. The characterization results of the regenerated catalysts showed that the specific surface area was restored 95% more than that of fresh catalyst. Under this study, the activity of the regenerated catalysts with acid solution (3~6 M) without using ultrasonic wave in a simulated in situ conditions was restored 90% more than that of the fresh catalyst. It was found that improved activity of regenerated catalyst was caused by removing the deactivating materials from the surface of the deactivated SCR catalyst through acid washing.

• Bulletin of the Korean Chemical Society
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• v.23 no.6
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• pp.803-807
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• 2002

The conversion of dimethyl ether(DME) has been carried out over $\gamma-alumina$, silica-alumina, and modified $\gamma-aluminal$ catalysts. Especially, the water effect has been investigated on purpose to develop a suitable catalyst for one-step synthesis of DME from $CO_2$ hydrgenation, The $\gamma-Al_2O_3$ modified with 1 wt% silica is more active and less deactivated by water than unmodified one. $CO_2has$ no effect on catalytic dehydration of methanol to DME.

• Applied Chemistry for Engineering
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• v.21 no.1
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• pp.104-110
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• 2010

Deactivation of SCR catalysts applied in coal, orimulsion, and LNG power plants in Korea were studied for the regeneration of the deactivated catalyst. The catalysts were characterized by XRD, ICP-AES, BET and SEM, and were examined for ammonia SCR. Deactivation of SCR catalyst applied in coal power plant was mainly caused by the blockade of the pore due to the deposition of sulfate and particulate related to the ingredients of the fuel. The surface area of SCR catalyst applied in orimulsion power plant decreased considerably by the accumulation of the compounds of vanadium, sulfur, and magnesium on the surface of the catalyst. The compounds of vanadium and sulfur were related to the ingredients of the fuel, and the compound of magnesium was related to the additive of the fuel. The activity of the deactivated catalyst for ammonia SCR, however, decreased slightly. Despite the long use for more than two-year, deactivation of SCR catalyst applied in LNG power plants hardly occurred.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.7 no.1
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• pp.81-98
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• 2013

Since Probabilistic Latent Semantic Analysis (PLSA) and Latent Dirichlet Allocation (LDA) were introduced, many revised or extended topic models have appeared. Due to the intractable likelihood of these models, training any topic model requires to use some approximation algorithm such as variational approximation, Laplace approximation, or Markov chain Monte Carlo (MCMC). Although these approximation algorithms perform well, training a topic model is still computationally expensive given the large amount of data it requires. In this paper, we propose a new method, called non-simultaneous sampling deactivation, for efficient approximation of parameters in a topic model. While each random variable is normally sampled or obtained by a single predefined burn-in period in the traditional approximation algorithms, our new method is based on the observation that the random variable nodes in one topic model have all different periods of convergence. During the iterative approximation process, the proposed method allows each random variable node to be terminated or deactivated when it is converged. Therefore, compared to the traditional approximation ways in which usually every node is deactivated concurrently, the proposed method achieves the inference efficiency in terms of time and memory. We do not propose a new approximation algorithm, but a new process applicable to the existing approximation algorithms. Through experiments, we show the time and memory efficiency of the method, and discuss about the tradeoff between the efficiency of the approximation process and the parameter consistency.

• Applied Chemistry for Engineering
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• v.9 no.1
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• pp.121-128
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• 1998

In fields of operating or handling a hydrogen isotope facility, and of the technology for nuclear fusion source management, gas chromatography has been used as one of the practical techniques lot separation and enrichment of hydrogen isotopic gases including tritium. Chromatographic separation experiments of the hydrogen isotope mixture (hydrogen, deuterium and tritium) were carried out by use of a commercially available gas chromatograph. An aliquot of gas sample was injected by a specially designed vacuum sampler into the stream of inert carrier gas which went through the separation column under liquid nitrogen temperature. The complete separation of hydrogen isotopic molecules was observed with an alumina adsorbent partially deactivated by coating with 10% manganese chlorine. In addition, fairly good separation conditions were obtained without any appearance of nuclear spin isomers with shorter retention time, which would be available for the practical applications of the hydrogen isotope separation and enrichment.

• BMB Reports
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• v.28 no.3
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• pp.254-260
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• 1995

Cytochrome oxidase was purified from bovine-heart mitochondria and its enzymatic properties were examined. The purified cytochrome oxidase was identified by its absorption spectrum and chromatogram through gel filtration. The specific activity, purification degree and yield of purified cytochrome oxidase were 18 nmol/mg/ml/min, 24.83 fold and 0.93%, respectively. The activity of the enzyme assayed by a ferrocytochrome $c-O_2$ system was optimized at $25^{\circ}C$ and pH 6.5. Examining the effect of nonionic detergents established that cytochrome oxidase was deactivated by Triton X-100. The oxidase was activated by Tween 80 and deactivated by Tween 20. The Michaelis constant and maximum velocity of the oxidase for ferrocytochrome c were 0.032~0.044 mM and 0.019~0.021 mM/min, respectively. After adaption to basal diet for a week, experimental diets containing 6 mg Cu/kg, or zero mg Cu/kg, or 12 mg Cu/kg were fed to a control group, a copper-free group and a copper-rich group of Sprague-Dawley rats, respectively, for 4 weeks. The specific activities assayed for the ferrocytochrome $c-O_2$ system of isolated cytochrome oxidase from the rat liver of control, copper-free, and copper-rich group were 1.00, 1.19, and 0.878 nmol/mg/ml/min, respectively. Their degrees of purification were 11.38, 10.82 and 8.78 fold, respectively. The specific activities for liver and heart mitochondrial cytochrome oxidase of copper-free/copper-rich groups assayed using the ferrocytochrome $c-O_2$ system were 81.4% and 96.4%/64.1% and 61.1%, respectively, compared with those of the control.

• Transactions of the Korean hydrogen and new energy society
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• v.1 no.1
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• pp.15-23
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• 1989

The selective separation of hydrogen from gas mixture containing hydrogen was experimentally studied using $LaNi_5$. The capacity and the rate of hydrogen separation, the purity of recovered hydrogen and the optimum condition of the regeneration of deactivated $LaNi_5$ were investigated. The separation rate and the recovery ratio of hydrogen were slowly decreased with the increase of the number of hydrogen absorption cycle. It was found that this result comes from the deactivation of $LaNi_5$ partly because of the blocking of hydrocarbon compounds in the $LaNi_5$ lattice and partly because of the poisoning of $LaNi_5$ surface by carbon monoxide contained in the gas mixture. The optimum condition for the regeneration of deactivated $LaNi_5$ was obtained by heating in a vacuum to about 637 K. The recovery ratio of hydrogen at the optimum condition was observed to be about 80%. The rates of hydrogen separation were measured in the ${\alpha}$-phase and two phase regions. The rate equations could be expressed as follows ; ${\alpha}$ - phase : $$-\frac{dP{_{H_2}}}{dt}=9.836{\times}10^{-3}(P{_{H_2}}_{-P_{eq}})$$ two phase region : $$-\frac{dP_{H{_2}}}{dt}=1.6909{\times}10^2\exp(-17560/RT)(P{_{H_2}}_{-P_{eq}})$$.