Chayoung Kim

Prof. Dr. Chayoung Kim

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Research Focus & Metrics

Academic Career Length

9Years (2018-Present)

(Calculated once Scilit publication data is synced: current year − year of first publication + 1)

Representative Publications

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27 April 2022 in Sustainability
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Journal Article
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Chayoung KimChayoung Kim
Chayoung Kim
Taejung ParkTaejung Park
Taejung Park
The purpose of this study is to explore the factors that have the most decisive influence on actual learning intention that leads to participation in adult education. For developing the predictive model, we used tree-based machine learning, with the longitudinal big data (2017~2020) of Korean adults. Based on the gradient boosting machine (GBM) results, among the eleven variables used, the most influential variables in predicting the possibility of lifelong education participation were self-pay education expenses and then highest level of education completed. After the grid search, not only the importance of the two variables but also the overall figures including the false positive rate improved. In future studies, it will be possible to improve the performance of the machine learning model by adjusting the hyper-parameters that can be directly set by less computational methods.

8 September 2020 in Sustainability
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Journal Article
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Taejung ParkTaejung Park
Taejung Park
Chayoung KimChayoung Kim
Chayoung Kim
The current study seeks to identify variables that affect the career decision-making of high school graduates with respect to the choice of university (re-)entrance in South Korea where education has great importance as a tool for self-cultivation and social prestige. For pattern recognition, we adopted a support vector machine with recursive feature elimination (SVM-RFE) with a big-data of survey of Korean college candidates. Based on the SVM-RFE analysis results, new enrollers were mostly affected by the mesosystems of interactions with parents, while re-enrollers were affected by the macrosystems of social awareness as well as individual estimates of talent and aptitude of individual systems. By predicting the variables that affect the high school graduates’ preparation for university re-entrance, some survey questions provide information on why they make the university choice based on interactions with their parents or acquaintances. Along with these empirical results, implications for future research are also presented.

10 March 2022 in International Journal of Precision Engineering and Manufacturing
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JSJonghwan Son
Jonghwan Son
Chayoung KimChayoung Kim
Chayoung Kim
MJMinjoong Jeong
Minjoong Jeong

14 October 2020 in Symmetry
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Chayoung KimChayoung Kim
Chayoung Kim
Owing to the complexity involved in training an agent in a real-time environment, e.g., using the Internet of Things (IoT), reinforcement learning (RL) using a deep neural network, i.e., deep reinforcement learning (DRL) has been widely adopted on an online basis without prior knowledge and complicated reward functions. DRL can handle a symmetrical balance between bias and variance—this indicates that the RL agents are competently trained in real-world applications. The approach of the proposed model considers the combinations of basic RL algorithms with online and offline use based on the empirical balances of bias–variance. Therefore, we exploited the balance between the offline Monte Carlo (MC) technique and online temporal difference (TD) with on-policy (state-action–reward-state-action, Sarsa) and an off-policy (Q-learning) in terms of a DRL. The proposed balance of MC (offline) and TD (online) use, which is simple and applicable without a well-designed reward, is suitable for real-time online learning. We demonstrated that, for a simple control task, the balance between online and offline use without an on- and off-policy shows satisfactory results. However, in complex tasks, the results clearly indicate the effectiveness of the combined method in improving the convergence speed and performance in a deep Q-network.

13 December 2021 in Symmetry
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Chayoung KimChayoung Kim
Chayoung Kim
Artificial intelligence (AI) techniques in power grid control and energy management in building automation require both deep Q-networks (DQNs) and deep deterministic policy gradients (DDPGs) in deep reinforcement learning (DRL) as off-policy algorithms. Most studies on improving the stability of DRL have addressed these with replay buffers and a target network using a delayed temporal difference (TD) backup, which is known for minimizing a loss function at every iteration. The loss functions were developed for DQN and DDPG, and it is well-known that there have been few studies on improving the techniques of the loss functions used in both DQN and DDPG. Therefore, we modified the loss function based on a temporal consistency (TC) loss and adapted the proposed TC loss function for the target network update in both DQN and DDPG. The proposed TC loss function showed effective results, particularly in a critic network in DDPG. In this work, we demonstrate that, in OpenAI Gym, both “cart-pole” and “pendulum”, the proposed TC loss function shows enormously improved convergence speed and performance, particularly in the critic network in DDPG.

13 October 2022 in Symmetry
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Journal Article
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Chayoung KimChayoung Kim
Chayoung Kim
Deep reinforcement learning (DRL) algorithms interact with the environment and have achieved considerable success in several decision-making problems. However, DRL requires a significant number of data before it can achieve adequate performance. Moreover, it might have limited applicability when DRL agents are able to learn in a real-world environment. Therefore, some algorithms combine DRL agents with supervised learning and leverage previous additional knowledge. Some have integrated a deep Q-learning network with a behavioral cloning model that can exploit supervised learning as prior learning. The algorithm proposed in this study is also based on these methods and is intended to update the loss function of the existing technique into a Bayesian approach. The supervised loss function used in existing algorithms and the loss function based on the Bayesian method proposed in this study differ in terms of the utilization of prior knowledge. Using prior knowledge and not using prior knowledge, such as the cross entropy being symmetric. As a result of the various OpenAI Gym environments, such as Cart-Pole and MountainCar, the learning convergence performance was improved. In particular, the proposed method can be applied to achieve fairly stable learning during the early stage when learning in a sparse environment is uncertain.