• Proceedings of the Korean Society of Machine Tool Engineers Conference
• /
• 2003.04a
• /
• pp.93-98
• /
• 2003

High speed precision machines have been introduced to the CNC industry in order to improve productivity, shorten the appointed date of delivery and reduce the prime cost. High speed machines have more functions then general machines, and they were proved in performance. The production and sales of the high speed machines have been increased not only in domestic market but also all over the world. Accordingly, machines are faster, there are lots of problems to be solved. One of the most difficult problems is the thermal displacement on the main spindle due to generated heat while the spindle is rotated in high speed. Since the thermal displacement directly effects the quality of the machined parts, utmost efforts to minimize the thermal displacement have to be given from the beginning of designing machines. In practice, variety of methods are attempted and practiced to minimize the thermal displacement such as design of symmetrical frame, adoption of high speed bearings, application of compensation system using non-contact sensor and use of forced circulating lubrication system with oil cooler. Even if these variable methods have been practically used in the industrial field, generated heat has not been Perfectly Prevented lienee, in this paper, the characteristics of thermal displacement were investigated when several kinds of oil were tested for a high speed machine with forced circulating lubrication system within the same atmosphere and under the same conditions.

• Transactions of the Korean Society of Machine Tool Engineers
• /
• v.13 no.2
• /
• pp.47-53
• /
• 2004

High speed precision machines have been introduced to the CNC industry in order to improve productivity, shorten the appointed date of delivery and reduce the prime cost. High speed machines have more functions then general machines, and they were proved in performance. The production and sales of the high speed machines have been increased not only in domestic market but also all over the world. Accordingly, machines are faster, there are lots of problems to be solved. One of the most difficult problems is the thermal displacement on the main spindle due to generated heat while the spindle is rotated in high speed. Since the thermal displacement directly effects the quality of the machined parts, utmost efforts to minimize the thermal displacement have to be given from the beginning of designing machines. In practice, variety of methods are attempted and practiced to minimize the thermal displacement such as design of symmetrical frame, adoption of high speed bearings, application of compensation system using non-contact sensor and use of forced circulating lubrication system with oil cooler. Even if these variable methods have been practically used in the industrial field, generated heat has not been perfectly prevented. Hence, in this paper, the characteristics of thermal displacement were investigated when several kinds of oil were tested for a high speed machine with forced circulating lubrication system within the same atmosphere and under the same conditions.

• Journal of Power Electronics
• /
• v.15 no.5
• /
• pp.1305-1317
• /
• 2015

Distributed generation systems (DGSs) have been getting more and more attention in terms of renewable energy use and new generation technologies in the past decades. The self-excited induction generator (SEIG) occupies an important role in the area of energy conversion due to its low cost, robustness and simple control. Unlike synchronous generators, the SEIG has to absorb capacitive reactive power from the outer device aiming to stabilize the terminal voltage at load changes. This paper presents a novel static VAR compensator (SVC) called a magnetic energy recovery switch (MERS) to serve as a voltage controller in SEIG powered DGSs. In addition, many small scale SEIGs, instead of a single large one, are applied and devoted to promote the generation efficiency. To begin with, an expandable mathematic model based on a d-q equivalent circuit is created for parallel SEIGs. The control method of the MERS is further improved with the objective of broadening its operating range and restraining current harmonics by parameter optimization. A hybrid control strategy is developed by taking both of the stand-alone and grid-connected modes into consideration. Then simulation and experiments are carried out in the case of single and double SEIG(s) generation. Finally, the measurement results verify that the proposed DGS with SVC-MERS achieves a better stability and higher feasibility. The major advantages of the mentioned variable reactive power supplier, when compared to the STATCOM, include the adoption of a small DC capacitor, line frequency switching, simple control and less loss.

• Journal of Advanced Marine Engineering and Technology
• /
• v.33 no.6
• /
• pp.880-885
• /
• 2009

The ships have a lot of electric machinery needed to supply electricity from the moment of launching coming out of dry dock to docking at jetty. Thus, the ships always have to use alternator and electric machinery that has low efficiency under the low load. Many government service ships like the MMU training ship have been spending lots of time at jetty rather than sailing at sea. These ships are operated under the condition of low load due to the operation of basic machinery at jetty and electric machineries are driven with the status of low efficiency. This paper would suggest the energy saving method for these ships. The investigation describes that shore connection is a great asset to these ships and that the flow rate control by adjusting revolution with the adoption of inverter is better than flow rate control by using throttle valve to save energy. The result is based on the investigation of cooling pump at MMU training ship.

• Korea Journal of Hospital Management
• /
• v.26 no.4
• /
• pp.12-28
• /
• 2021

Purposes: The convenience of smartphones have lead to people's overdependence on devices, which may cause obstacles in daily life. It is useful to manage smartphone overdependence by using mobile health applications. We aimed to investigate the acceptance of mobile health applications designed to help in the management of smartphone overdependence. Methodology/Approach: We developed the extended model based on the Unified Theory of Acceptance and Use of Technology 2. The modified model had six hypotheses with six variables: result demonstrability, performance expectancy, effort expectancy, social influence, perceived risk, and behavioral intention to use. We randomly included 425 smartphone users in an online survey in 2020. A structural equation model was used to estimate the significance of the path coefficients. Findings: Performance expectancy and social influence had a very strong direct positive association with behavioral intention to use. Result demonstrability had a direct positive association with performance expectancy. Perceived risk had a strong direct negative association with performance expectancy. Performance expectancy and social influence were the main factors directly influencing the acceptance of mobile health applications for the management of smartphone overdependence. Practical Implications: We demonstrated smartphone users' acceptance of mobile health applications for smartphone overdependence management. Based on these results, we could develop mobile health applications more effectively.

• Journal of Digital Convergence
• /
• v.15 no.6
• /
• pp.71-82
• /
• 2017

Most banks in Myanmar have begun to provide their services via mobile phones. However, few studies investigated the factors that may help to set mobile services from a customer perspective. So, this study aims to propose and test a conceptual research model to predict the user's intention to use and actual use level of mobile banking service by combining UTAUT and DeLone-Mclean IS model. Data were collected from 206 citizens who had experienced mobile banking in various regions of Myanmar. The study found that performance expectancy, effort expectancy, information quality and service quality influence the user 's intention to adopt mobile banking services which directly affects the user's actual use of them. However, social influence, facilitating condition and system quality don't influence the user's intention. The study results contribute to meeting customer's needs and reducing customer risk in Myanmar's mobile banking industry, suggesting to seamlessly provide the necessary resources like technology improvements, organizational infrastructure and service centers. Another future study are required to include service's security and trust factors so that the service providers could gain their customers' reliability and trust.

• The Journal of the Korea Contents Association
• /
• v.20 no.10
• /
• pp.284-293
• /
• 2020

The rapid progress of AI technology gives us the expectation to solutions to various problems in our society, and at the same time, it gives us anxiety about the side effects that can occur if AI develops beyond human control. This study was conducted in the early 20s with less objection to advanced devices. We attempted to provide clues to understand thoughts and attitudes of the targets about the future environment that will be brought by AI through the process of finding intent the acceptance of strong AI technology. For this, we applied the Theory of Planned Behavior, and further expanded this research model to identify factors affecting the attitude toward AI. As a result, the attitude toward AI and perceived behavioral control had a significant effect on the intention to use to strong AI. In addition, we found that the expectation of the benefit of improving task performance and the anxiety on the threat of relationship disturbance had a significant effect on the attitude toward AI. This study suggests implications for AI-related companies establishing the direction of technology development and for government setting a policy direction for AI adoption.

• Journal of Power Electronics
• /
• v.15 no.1
• /
• pp.146-159
• /
• 2015

Since the power capacity needed for the propulsion of large ships is very large, a multiphase AC induction propulsion mode is generally adopted to meet the higher requirements of reliability, redundancy and maintainability. This paper gives a detailed description of the development of a 20MW fifteen-phase PWM driver for advanced fifteen-phase propulsion induction motors with a special third-harmonic injection in terms of the main circuit hardware, control system design, experiments, etc. The adoption of the modular design method for the main circuit hardware design can make the enclosed mechanical structure simple and maintainable. It can also avoid the larger switch stresses caused by the multiple turn on of the IGBTs in conventional large-capacity converter systems. The use of the distributed controller design method based on a high-speed fiber-optic ring net for the control system can overcome such disadvantages as the poor reliability and long maintenance times arising from the conventional centralized controller which is designed according to point-to-point communication. Finally, the performance of the 20MW PWM driver is verified by experimentation on a new fifteen-phase induction propulsion motor.

• The Journal of the Korea Contents Association
• /
• v.22 no.3
• /
• pp.17-34
• /
• 2022

Although NFTs are a new technology with a fast-growing industry, the studies for consumer protection and promotion are insufficient. Thus, this study analyzes the relationship of variables that affect intention to use NFT based on the UTUAT model, additionally, moderating effect of NFT types and crypto investment experience. Subjects of this study are limited to potential NFT users. The independent variables such as performance expectations, network externality, and innovation are statistically significant, however, the moderating effect is not suggested. With low awareness, the tendencies of subjects lead to adoption rather than technical understanding.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• v.18 no.8
• /
• pp.2417-2430
• /
• 2024

The need for secure user authentication in blockchain-based applications has been growing with the increased adoption of Decentralized Identity (DID) credentials in blockchain. Zokrates, a tool designed to protect user privacy within smart contracts, had a limitation in that it could not accept authenticated user information such as credentials, only allowing the use of manually inputted data. In this paper, we propose a smart contract system that securely validates DID credentials to overcome the limitations of traditional centralized authentication systems. This system ensures the safe identification of users within blockchain-based applications by authenticating their identities in a trusted manner within the blockchain. As the demand for user authentication in blockchain rises, this paper emphasizes the significance of a blockchain-based identity verification system that guarantees both privacy and security. Leveraging the Zero-Knowledge Proof method and utilizing the Zokrates tool, this innovative approach aims to provide solutions for the digital identity verification process, thereby expanding the scope of blockchain technology applications. Moreover, we also provide a CLI for each entity. We help anyone who wants to authenticate their identity using the tool to safely verify it on-chain.