• Transactions of the Korean hydrogen and new energy society
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• v.30 no.4
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• pp.347-355
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• 2019

As a solution to the growing concern on the global warming, researches are being actively carried out to apply carbon dioxide capture and storage technology to power generation systems. In this study, the integrated gasification combined cycle (IGCC) adopting oxy-combustion carbon capture was modeled and the effect of replacing the conventional air separation unit (ASU) with the ion transport membrane (ITM) on the net system efficiency was analyzed. The ITM-based system was predicted to consume less net auxiliary power owing to an additional nitrogen expander. Even with a regular pressure ratio which is 21, the ITM-based system would provide a higher net efficiency than the optimized ASU-based system which should be designed with a very high pressure ratio around 90. The optimal net efficiency of the ITM-based system is more than 3% higher than that of the ASU-based system. The influence of the operating pressure and temperature of the ITM on system efficiency was predicted to be marginal.

• Korean Chemical Engineering Research
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• v.50 no.3
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• pp.516-521
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• 2012

This study developed a simple model to investigate effects of important operating parameters on performance of a bubbling-bed adsorber and regenerator system collecting $CO_2$ from flue gas. The chemical reaction rate was used with mean particles residence time of a reactor to determine the extent of conversion in both adsorber and regenerator reactors. Effects of process parameters - temperature, gas velocity, solid circulation rate, moisture content of feed gas - on $CO_2$ capture efficiency were investigated in a laboratory scale process. The $CO_2$ capture efficiency decreased with increasing temperature or gas velocity of the adsorber. However, it increased with increasing the moisture content of the flue gas or the regenerator temperature. The calculated $CO_2$ capture efficiency agreed to the measured value reasonably well. However the present model did not agree well to the effect of the solid circulation rate on $CO_2$ capture efficiency. Better understanding on contact efficiency between gas and particles was needed to interpret the effect properly.

• Geomechanics and Engineering
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• v.25 no.4
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• pp.341-345
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• 2021

1D sand compression response to ko-loading experiences volume contraction from low to high effective stress regimes. Previous study suggested compressibility model with physically correct asymptotic void ratios at low and high stress levels and examined only for both remolded clays and natural clays. This study extends the validity of Enhanced Terzaghi model for different sand types complied from 1D compression data. The model involved with four parameters can adequately fit 1D sand compression data for a wide stress range. The low stress obtained from fitting parameters helps to identify the initial fabric conditions. In addition, strong correlation between compressibility and the void ratio at low stress facilitates determination of self-consistent fitting parameters. The computed tangent constrained modulus can capture monotonic stiffening effect induced by an increase in effective stress. The magnitude of tangent stiffness during large strain test should not be associated with small strain stiffness values. The use of a single continuous function to capture 1D stress-strain sand response to ko-loading can improve numerical efficiency and systematically quantify the yield stress instead of ad hoc methods.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.17 no.2
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• pp.99-113
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• 1992

In general, TDMA and FDMA have been used for multiple access communication methods. Recently. However, ALOHA and CSMA protocols came to exist as new schemes for VSAT data networks and LANs, respectively. These schemes are proven to be effective for packet switched communication systems that has bursty traffic but packet collisions. In this paper we analyze capture statistics arising from fading channels in packet radio communication systems in the context of ALOHA protocol. We derive general results of the exact form of capture probabilities and present numerical data for wide range of fading parameters. Since the capture probabilities are found to approach zero when the number of transmitted signals become larger, we are able to determine the achievable channel throughput by a least squares fitting of an exponential-type function to the probabilities.

• The Korean Journal of Applied Statistics
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• v.35 no.4
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• pp.501-515
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• 2022

Despite the stylized statistical features of returns of financial returns such as fat-tailed distribution and leverage effect, no stochastic volatility models that can explicitly capture these features have been presented in the existing frequentist approach. we propose an approximate parameterization of stochastic volatility models that can explicitly capture the fat-tailed distribution and leverage effect of financial returns and a maximum likelihood estimation of the model using Langrock et al. (2012)'s hidden Markov model approximation in a frequentist approach. Through extensive simulation experiments and an empirical analysis, we present the statistical evidences validating the efficacy and accuracy of proposed parameterization.

• Journal of Korean Society of Environmental Engineers
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• v.39 no.11
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• pp.607-612
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• 2017

The effect of carbonic anhydrase on $CO_2$ absorption rates and the heat of reaction were evaluated in various amine solutions for post combustion $CO_2$ capture process. The $CO_2$ absorption rate was analyzed in 30 wt% MEA, AMP, DMEA, MDEA aqueous solutions with and without carbonic anhydrase (250 mg/L) from bovine erythrocyte. $CO_2$ absorption rates were increased in all solutions with carbonic anhydrase. The effect of carbonic anhydrase on absorption rates was more in tertiary amine (DMEA and MDEA) solutions than in primary amine (MEA) and hindered amine (AMP) solutions. The heat of reaction of MEA, DMEA, MDEA aqueous solutions with and without carbonic anhydrase were measured using reaction calorimeter. Carbonic anhydrase decreased the heat of absorption in all solutions. The results suggested that tertiary amines that have the excellent desorption ability were suitable for applying carbonic anhydrase to the post combustion $CO_2$ capture process and the effect of carbonic anhydrase was best in MDEA solution.

• Applied Chemistry for Engineering
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• v.17 no.1
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• pp.44-51
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• 2006

Effects of multiple-cycle operation and $SO_2$ concentration on $CO_2$ capture characteristics of three limestones were investigated in a fluidized bed reactor. For each of these sorbents, the measured $CO_2$ capture capacity decreased as the number of cycles increased and as the $SO_2$ concentration increased. On the other hand, the $SO_2$ capture increased with the increased number of cycles and the $SO_2$ concentration. The total calcium utilization decreased as the number of cycles increased, but the effect of $SO_2$ concentrations on the total calcium utilization depended on the type of limestone. For Strassburg limestone, the total calcium utillization decreased with increasing $SO_2$ concentration. However, for Luscar and Danyang limestones, the total calcium utilization was almost independent of $SO_2$ concentration for the range investigated. The results showed that $SO_2$ in flue gas reduced the $CO_2$ capture capacity of limestone and that the sulfation pattern affected the $CO_2$ capture capacity.

• Korean Journal of Applied Biomechanics
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• v.23 no.2
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• pp.91-97
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• 2013

The purpose of this study was to compare the effect of a new warm-up condition, overloaded arm weights (721 g each arm, [OA]), on the bat speed during warm-up and immediately after warm-up with traditional warm-up conditions such as no-extra mass warm-up (control condition, [CO]) and overloaded bat warm-up (885 g donut on a bat, [OB]) conditions. Twenty male subjects who had competitive baseball experience participated in this study. Electromagnetic motion capture system was used to capture body segment motions. Results indicated that the OB showed significantly slower bat speed than the CO and OA did during warm-up (p<.05) and the bat speeds of OA and OB were similar. There was no main effect of different types of warm-up condition on the bat speed at post-warm-up swings. However, the first trial immediately after the OA and OB showed significant slower than the later trials (p<.05). Conclusively, the overloaded arm weights and overloaded bat did not show statistical superiority than the standard warm-up conditions in the deck circle and recovery time more than 3 minutes after loaded warm-up is recommended.

• Journal of Ecology and Environment
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• v.34 no.4
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• pp.357-363
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• 2011

To examine factors affecting feeding efficiency of grey herons (Ardea cinerea), the foraging behavior was studied at a reservoir in Asan city, Chungcheongnam-do, South Korea during the breeding seasons (from April to July) of 2006 and 2007. Four factors (age of foraging birds, time of day, breeding stage, and microhabitat type) were analyzed. Adults were more efficient foragers than recently fledged juveniles, and they had a higher success rate than juveniles. About half of the adults caught large prey, whereas most juveniles caught only small prey. Adult grey herons had different feeding efficiency according to the breeding stage. Pecking and capture rates were high during the late period (fledging stage), and biomass intake rates were high during the early (incubating stage) and late periods. However, time of day had no significant effect on foraging activity of adult grey herons. Feeding activities of adult grey herons also showed significant variation among microhabitat types. Pecking and capture rates were higher in the submerged plants area, but capture success rate and biomass intake rate were not different according to microhabitat type.

• Journal of Korea Game Society
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• v.16 no.6
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• pp.173-184
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• 2016

This research explores strategy for game developers to select platforms in the game industry where are traditional two-sided market focusing on mobile game platforms. We conducted content qualitative analysis by collecting data through contents on online and offline and interviewed four CEO of game developers to secure validity and reliability as well. The results of the research are the following: First, platforms selection factors of game developers are game implementation ability and technical stability, marketing competence of platforms, and profitability creation. Second. the initiative of mobile game platforms has handed over from first generation of mobile games to second mobile games according to their value creation and value capture.