• The Journal of Korea Robotics Society
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• v.17 no.3
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• pp.308-313
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• 2022

This paper proposes a velocity control method for a permanent magnet synchronous motor (PMSM) based on the Koopman operator that does not require model parameter information except for pole-pair of the motor and external load. First, the Koopman operator is derived using observable functions and observation data. Then, the desired q-axis current corresponding to the desired velocity is generated using the relationship between the continuous-time Koopman operator and the dynamics of PMSM. Also, the dynamic equation of PMSM is expressed as a linear form in observable space using the discrete-time Koopman operator. Finally, it is applied to the linear quadratic regulator (LQR) to derive the final form of control input. To verify the proposed method, the conventional cascade PI controller and the LQR controller configured with the existing technique are compared with the proposed method in the viewpoint of q-axis current generation and velocity tracking performance in an environment with noise and external load.

• Journal of the Korea Society of Computer and Information
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• v.27 no.8
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• pp.169-176
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• 2022

With the continuous development of technologies related to 5G, artificial intelligence, and autonomous vehicle systems, standards and services for V2X and C-ITS environments are being studied a lot. BSM (basic safety message) was adopted as a standard for exchanging data between vehicles based on data collected and generated by vehicle systems in a V2V environment. In this paper, we propose a framework that can safely store BSM messages and effectively check the stored messages using Event-Sourcing and CQRS patterns. The proposed framework can securely store and manage BSM messages using hash functions. And it has the advantage of being able to check the stored BSM data in real time based on the time series and to reproduce the state.

• Journal of Forest and Environmental Science
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• v.39 no.1
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• pp.40-48
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• 2023

Street trees have been incorporated into urban forests to regulate the microclimate and provide shade as well as provide aesthetic and environmental functions and to evaluate their physiological characteristics. Zelkova serrata is a major tree species that has been planted on various South Korean streets. We determined the physiological characteristics of Z. serrata in street trees of Goyang and Paju in Gyeonggi Province. According to survey sites, net CO₂ assimilation rates was 13.9-16.4 µmol CO₂ m^-2s^-1, chlorophyll fluorescence (Fv/Fm) was 0.80-0.82, and proline contents was showed 3.4-3.7 mg g^-1 FW. The studied trees were assumed to be physiologically stressed, but it was found that Z. serrata was planted as street trees were not significantly stressed when compared to chlorophyll fluorescence responses and proline contents. In the future, the continuous monitoring system is needed to evaluate the physiological characteristics of urban trees.

• Journal of People, Plants, and Environment
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• v.22 no.3
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• pp.279-287
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• 2019

This study carried out a horticultural program for people with mental disabilities to determine suitability of the horticultural activity program and to actually apply to vocational rehabilitation. The program was carried out in 16 sessions from April 12 to June 7, 2018 with nine people with a strong will to participate in vocational rehabilitation at a health center for persons with mental disabilities. The tools used were the Horticultural Activity Performance Assessment (psychological behavior) and Purdue Pegboard Test that examines functions of hands and arms. The subjects sold the products they made during class time and obtained the profits. After the program, the scores increased with a significant difference (p = .000) in the psychological behavior area of the Horticultural Activity Performance Assessment. Hand and arm movement also showed continuous improvement along the program with a significant difference (p = .000), as well as finger dexterity also with a significant difference (p = .018). The net profit was 314,000 KRW (subtracting cost of goods 314,000 KRW from total sales 628,000 KRW). The profit was shared equally among the nine subjects, each receiving 34,900 KRW. Therefore this study proved horticultural activity class is suitable for vocational rehabilitation of people with mental disabilities proved by the positive effects. We also expect that the subjects will be able to make more profits if they learn more skills, since they are interested the process of making such profits.

• Steel and Composite Structures
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• v.45 no.3
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• pp.331-348
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• 2022

The main goal of this article is to develop the finite element formulation based on the nonlocal strain gradient and the refined higher-order deformation theory employing a new function f(z) to investigate the static bending and free vibration of functionally graded porous (FGP) nanobeams. The proposed model considers the simultaneous effects of two parameters: nonlocal and strain gradient coefficients. The nanobeam is made by FGP material that exists in un-even and logarithmic-uneven distribution. The governing equation of the nanobeam is established based on Hamilton's principle. The authors use a 2-node beam element, each node with 8 degrees of freedom (DOFs) approximated by the C¹ and C² continuous Hermit functions to obtain the elemental stiffness matrix and mass matrix. The accuracy of the proposed model is tested by comparison with the results of reputable published works. From here, the influences of the parameters: nonlocal elasticity, strain gradient, porosity, and boundary conditions are studied.

• Human Ecology Research
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• v.61 no.3
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• pp.475-492
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• 2023

This study investigated player responses to microtransactions in freemium Massively multiplayer online roleplaying games (MMORPG), specifically focusing on the game LostArk using English language review data. To this end, structural topic modeling was employed and the following six microtransaction-relevant topics were identified: microtransactions, developer issues, real money trade (RMT), random number generator (RNG) upgrade system, game content, and collectibles & adventure. The first four topics were classified as being "not recommended". However, the proportions of microtransaction-related topics were relatively lower than the other topics. Additionally, this study did not extract keywords related to unfairness and unethical issues in previous microtransaction research. The last two topics, game content, and collectibles & adventure were "recommended" topics, indicating positive functions of microtransactions such as enhancing the game experience by purchasing virtual items. Moreover, it was found that players who do not engage in microtransactions can still be satisfied through continuous game content updates. Additionally, an examination of the interaction effect between time and recommendation status revealed that while the frequency with which the six microtransaction-related topics were mentioned increased over time in the reviews, the ratio of recommendations to non-recommendations varied differently. This study contributes to game-related research by revealing players' authentic opinions on microtransactions in freemium MMORPGs, thereby providing practical implications for game companies.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.23 no.6
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• pp.69-74
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• 2023

In this paper we review techniques for building and analyzing wavelets on irregular point sets in one and two dimensions. In particular we focus on subdivision schemes and commutation. Subdivision means the skill that approximates the initial lines or mesh into a tender curve or a curved surface by continuous partitioning operation. The key to generalizing wavelet constructions to non-traditional settings is the use of generalized subdivision. The first generation setting is already connected with subdivision schemes, but they become even more important in the construction of second generation wavelets. Subdivision schemes provide fast algorithms, create a natural multi-resolution structure, and yield the underlying scaling functions and wavelets we seek.

• Journal of Korea Water Resources Association
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• v.37 no.7
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• pp.541-552
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• 2004

In this paper, ascending functions of the pool-and-weir fishway which has been established for the upstream migration of migratory fish at Jamsil Weir in the lower part of the Han River was assessed by applying tile Existing Fishway Measurement Method, and measures to improve these functions were suggested. The primary fish which ascended the fishway during the period of measurement was Erythroculter erythropterus Basilewsky, greater than 29cm in the body length. A total of 361 individual fish were collected with traps established at the exit of the fishway The maximum ascending capacity for the fish was 2.53${\times}$10^{-3}$ fish/hr/g. The fishway of Jamsil Weir does not satisfy the various fish species inhabiting in the river. Especially, small fishes of lower swimming ability may not ascend the fishway because the difference in water levels between upper and lower pools in the fishway was too large at the exit and there was too much discharge flowing into the fishway. This fishway does not have a roll in the ascending function for other species except Erythroculter erythropterus Basilewsky and Hemibarbus labeo Pallas, for which swimming ability is great. In order to improve the ascending function of the fishway, the structures of the fishway need to be changed so that various species in the river can easily ascend and the fishway function be taken into consideration in operation of the gates of the weir. Additional construction of fishways on both sides of the lower flow channel are needed to correct a decline in the fishway effectiveness due to continuous flow over the fixed part of the weir.

• The Korean Journal of Applied Statistics
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• v.22 no.3
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• pp.595-606
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• 2009

Two tests were introduced for comparing several survival functions with doubly interval-censored data and illustrated with data surveyed by Korean Cancer Prevention Study (Jee et al., 2005). The test which extended Kim et al. (2006)'s test to the doubly interval-censored data has an advantage over Sun (2006)'s test in terms of saving computation time because the proposed test only depends on the size of risk set, and also the proposed test is applicable to continuous failure time data as well as discrete failure time data unlike Sun's test. Comparing male with female groups on the incubation time of diabetes was highly different and the survival of female group was longer than that of male one. Regardless of gender, the difference in survival functions of four age groups was highly significant with p-value of less than 0.001. This trend was more remarkable for female group than for male one. Simulation results showed that the significance level of both tests was well controlled and the proposed test was better than Sun's test in terms of power.

• Journal of the Korean Institute of Intelligent Systems
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• v.18 no.1
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• pp.32-40
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• 2008

Fuzzy rules are very useful and efficient to describe classification rules especially when the attribute values are continuous and fuzzy in nature. However, it is generally difficult to determine membership functions for generating efficient fuzzy classification rules. In this paper, we propose a method of automatic generation of efficient fuzzy classification rules using evolutionary algorithm. In our method we generate a set of initial membership functions for evolutionary algorithm by supervised clustering the training data set and we evolve the set of initial membership functions in order to generate fuzzy classification rules taking into consideration both classification accuracy and rule comprehensibility. To reduce time to evaluate an individual we also propose an evolutionary algorithm with data partition evaluation in which the training data set is partitioned into a number of subsets and individuals are evaluated using a randomly selected subset of data at a time instead of the whole training data set. We experimented our algorithm with the UCI learning data sets, the experiment results showed that our method was more efficient at average compared with the existing algorithms. For the evolutionary algorithm with data partition evaluation, we experimented with our method over the intrusion detection data of KDD'99 Cup, and confirmed that evaluation time was reduced by about 70%. Compared with the KDD'99 Cup winner, the accuracy was increased by 1.54% while the cost was reduced by 20.8%.