• Journal of Korean Society of Industrial and Systems Engineering
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• v.36 no.1
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• pp.24-35
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• 2013

A cell formation approach based on cluster analysis is developed for the configuration of manufacturing cells. Cell formation, which is to group machines and parts into machine cells and the associated part families, is implemented to add the flexibility and efficiency to manufacturing systems. In order to develop an efficient clustering procedure, this paper proposes a cluster analysis-based approach developed by incorporating and modifying two cluster analysis methods, a hierarchical clustering and a non-hierarchical clustering method. The objective of the proposed approach is to minimize intercellular movements and maximize the machine utilization within clusters. The proposed approach is tested on the cell formation problems and is compared with other well-known methodologies available in the literature. The result shows that the proposed approach is efficient enough to yield a good quality solution no matter what the difficulty of data sets is, ill or well-structured.

• The Bulletin of The Korean Astronomical Society
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• v.43 no.2
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• pp.40.3-40.3
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• 2018

This dissertation presents the results on two-dimensional Redshift space distortion (hereafter RSD) analyses of the large-scale structure of the universe using spectroscopic data and on improvement of modeling of the RSD effect. RSD is an effect caused by galaxies' peculiar velocity on their clustering feature in observation along the line of sight and is thus intimately connected to the growth rate of the structure in the universe, from which we can test the origin of cosmic acceleration and Einstein's theory of gravity at cosmic scales in the end. However, there are several challenges in modeling precise and accurate RSD effect, such as non-linearities and the existence of an exotic component, e.g. massive neutrino. As part of endeavors for modeling more precise and accurate galaxy clustering in redshift space, this dissertation includes a series of works for this issue. (More detailed descriptions were omitted.)

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.15 no.3
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• pp.853-873
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• 2021

In recent years, deep reinforcement learning (DRL) models are enjoying great interest as their success in a variety of challenging tasks. Deep Q-Network (DQN) is a widely used deep reinforcement learning model, which trains an intelligent agent that executes optimal actions while interacting with an environment. This model is well known for its ability to surpass skilled human players across many Atari 2600 games. Although DQN has achieved excellent performance in practice, there lacks a clear understanding of why the model works. In this paper, we present a visual analytics system for understanding deep Q-network in a non-blind matter. Based on the stored data generated from the training and testing process, four coordinated views are designed to expose the internal execution mechanism of DQN from different perspectives. We report the system performance and demonstrate its effectiveness through two case studies. By using our system, users can learn the relationship between states and Q-values, the function of convolutional layers, the strategies learned by DQN and the rationality of decisions made by the agent.

• KDI Journal of Economic Policy
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• v.44 no.2
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• pp.29-44
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• 2022

This study compares the wage equation in Korea to those in other countries, focusing on the wage returns to adult education and training (AET) participation. It is found that the wage compensation structure in Korea is associated mainly with job characteristics such as tenure and workplace size rather than with worker characteristics such as AET participation and cognitive abilities. It is also found that Korea's AET participation is skewed toward non-job-related AET, relative to the situations in other countries. These findings imply that the link between a worker's productivity and wage should be strengthened in order to incentivize workers to invest in AET relevant to the labor market.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2022.05a
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• pp.592-593
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• 2022

Masks have become a matter of course in life, and overseas travel, which I could always go, has become a fear. Company work, school classes, and concerts, which were essential to face-to-face, have been changed to non-face-to-face, and it has become possible in metaverse space through advanced technology. And various attempts have come into our daily lives.

• Journal of Astronomy and Space Sciences
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• v.40 no.1
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• pp.29-33
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• 2023

An unexplained acceleration on the order of 10^-8 cm s^-2, which is close to cH, where c is the speed of light and H is the Hubble constant, is detected in gravitationally bound systems of different scales, from the solar system to clusters of galaxies. We found that any test body located inside a fractal structure with fractal dimension D = 2 experiences acceleration of the same order and confirmed the previous work that photons propagating through this structure decrease the frequency owing to gravitational redshift. The acceleration can be directed against the movement of the test body. The fractal distribution of the matter should be at scales of at least hundreds of megaparsecs to a few gigaparsecs for the existence of this acceleration.

• The Bulletin of The Korean Astronomical Society
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• v.44 no.2
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• pp.59.2-59.2
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• 2019

In this talk, I will explain the implications of a rapid appearance of dark energy between the redshifts ($z$) of one and two on the expansion rate and growth of perturbations. Using both Gaussian process regression and a parametric model, I show that this is the preferred solution to the current set of low-redshift ($z<3$) distance measurements if $H_0=73~\rm km\,s^{-1}\,Mpc^{-1}$ to within 1\% and the high-redshift expansion history is unchanged from the $\Lambda$CDM inference by the Planck satellite. Dark energy was effectively non-existent around $z=2$, but its density is close to the $\Lambda$CDM model value today, with an equation of state greater than $-1$ at $z<0.5$. If sources of clustering other than matter are negligible, we show that this expansion history leads to slower growth of perturbations at $z<1$, compared to $\Lambda$CDM, that is measurable by upcoming surveys and can alleviate the $\sigma_8$ tension between the Planck CMB temperature and low-redshift probes of the large-scale structure.

• Korea Trade Review
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• v.45 no.2
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• pp.17-29
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• 2020

This study analyzed that the effects of AEO MRA benefit on decreasing of trade cost and the strategies for expanding of trade. It uses the system GMM for effective solutions of endogenous matter with lagged dependent variable. In terms of the result of analysis, AEO MRA has a positive effect on decreasing of trade cost, especially this study proved the result of previous study AEO MRA expanded the trade through improving the time required for customs clearance and deregulation of non-tariff barriers. In conclusion, this study proposes the policy fo AEO MRA by analyzing the trade cost of AEO MRA by using the system GMM.

• Journal of Environmental Health Sciences
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• v.37 no.1
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• pp.44-49
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• 2011

Under the Enforcement Rules of the National Health Promotion Act, smoking areas in coffee shops in Korea should be divided off from other areas. The effect on indoor air quality of different division types for smoking areas was evaluated. Using real-time monitors, fine particulate matter <2.5 ${\mu}m$ in diameter ($PM_{2.5}$) concentrations were measured simultaneously in the smoking and non-smoking areas of 30 coffee shops in Seoul. Average $PM_{2.5}$ concentrations in smoking and non-smoking areas were 132 ${\mu}g/m^3$ and 52 ${\mu}g/m^3$, respectively; significantly different. Average $PM_{2.5}$ concentrations in non-smoking areas were 39 ${\mu}g/m^3$ in the glass-wall type and 64 ${\mu}g/m^3$ in the separate-floor type. These $PM_{2.5}$ levels were above the US national ambient air quality standard of 35 ${\mu}g/m^3$. Although indoor $PM_{2.5}$ levels in non-smoking areas were reduced by the division, the rates of reduction were not significantly different by division type. Our results demonstrated that $PM_{2.5}$ from smoking areas can infiltrate into non-smoking areas. Therefore, a complete indoor smoking ban in coffee shops is the only way to protect customers and workers in non-smoking areas.

• Asian-Australasian Journal of Animal Sciences
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• v.28 no.10
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• pp.1419-1426
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• 2015

This study aimed to investigate the effect of the ratio of non-fibrous carbohydrates to neutral detergent fibre (NFC/NDF) and undegraded dietary protein (UDP) on rumen fermentation and nitrogen metabolism in lambs. Four $Dorper{\times}thin-tailed$ Han crossbred lambs, averaging $62.3{\pm}1.9kg$ of body weight and 10 mo of age, were randomly assigned to four dietary treatments of combinations of two levels of NFC/NDF (1.0 and 1.7) and two levels of UDP (35% and 50% of crude protein [CP]). Duodenal nutrient flows were measured with dual markers of Yb and Co, and microbial N (MN) synthesis was estimated using $^{15}N$. High UDP decreased organic matter (OM) intake (p = 0.002) and CP intake (p = 0.005). Ruminal pH (p<0.001), ammonia nitrogen ($NH_3-N$; p = 0.008), and total volatile fatty acids (p<0.001) were affected by dietary NFC/NDF. The ruminal concentration of $NH_3-N$ was also affected by UDP (p<0.001). The duodenal flow of total MN (p = 0.007) was greater for lambs fed the high NFC/NDF diet. The amount of metabolisable N increased with increasing dietary NFC:NDF (p = 0.02) or UDP (p = 0.04). In conclusion, the diets with high NFC/NDF (1.7) and UDP (50% of CP) improved metabolisable N supply to lambs.