• Proceedings of the KIPE Conference
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• 2011.07a
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• pp.444-446
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• 2011

A bidirectional dual active converter with the power factor control capability is proposed as a battery charger. The source side half-bridge acts as a PWM converter that maintains the unity power factor. The battery side half-bridge converter acts as a dual active bridge (DAB) together shares the same DC link voltage with PWM converter. The imbalance voltage phenomenon is eliminated by employing asymmetric duty cycle technique. Simulation results are included to verify theoretical analysis.

• Physical Therapy Korea
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• v.25 no.4
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• pp.27-36
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• 2018

Background: We developed a novel integrative lumbar stabilization technique that combines lumbar extension (LE) exercise with abdominal drawing-in maneuver (ADIM) to ameliorate low back pain (LBP) associated with neuromuscular imbalance and instability, based on the collective evidence of contemporary spinal rehabilitation. Objects: The specific aim of the present study was to investigate the effects of LE exercise with and without ADIM on core muscle strength, lumbar spinal instability, and pain, as well as functional characteristics in individuals with LBP using advanced radiographic imaging techniques. Methods: patients with mechanical LBP (N = 40, 6 males; $35.1{\pm}7.6years$) were recruited and randomly assigned either to the combined LE and ADIM (experimental group) or the LE alone (control group). Outcome measures included the visual analog scale, the modified Oswestry Disability Index, muscle strength imbalance (MSI), and radiographic imaging. The lumbar intervertebral displacement (LID), intervertebral (IV) and total lumbar extension (TLE) angles were calculated to evaluate the lumbar segmental instability. Results: The experimental group showed significant differences in the L3-L4, L5-S1 LIDs, L4-L5 and L5-S1 IV angles, and TLE angle as compared to the controls (p<.05). Immediate pain reduction and muscle strength imbalance ratio were significantly different between the groups (p<.05). Conclusion: These results suggest that the addition of ADIM significantly increased lumbar spinal stabilization in individuals with LBP, thereby reducing pain associated with functional lumbar flexion during daily activities.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.66 no.11
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• pp.1584-1590
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• 2017

This paper presents a implementation method of reliable speed limitation controller considering motor parameter variation in high speed operation. In spinning process of drum washing machine, speed increase has to be limited when unallowable imbalance mass is detected. Otherwise, severe noise and vibration can happen because noise and vibration are proportional to imbalance mass. To detect imbalance mass, d-axis current magnitude is used. However, we have to compensate for back-emf and power supply variation by means of detecting them because d-axis current is affected by both of them. On the other hand, we have to carefully estimate back-emf because back-emf is affected by stator resistance variation and inverter voltage error. Stator resistance variation can happen by manufacturing process for mass production or temperature variation in running. And there are inverter voltage errors between command voltage from micro-computer to inverter and real voltage from inverter to motor because of rising and falling time delay and turn-on resistance of power semiconductor switch. To solve this problem, we propose 2-step align current injection method which is to inject step-wise current right before starting. By this method, we can simply obtain stator resistance by ratio of voltage without inverter voltage error and current, and we can measure inverter voltage error. So we can obtain more exact model current, and then by simple calculation with compensation gain, we can estimate more accurate motor back-emf. We show that this method works well. It is verified through experiments.

• Safety and Health at Work
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• v.8 no.1
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• pp.77-83
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• 2017

Background: In contemporary China, most parents are dual-earner couples and there is only one child in the family. We aimed to examine the associations of parents' work stress with suicidal ideation among the corresponding adolescent. We further hypothesized that low parental support experienced by adolescents may mediate the associations. Methods: Cross-sectional data from school students and their working parents were used, with 907 families from Kunming City, China. Stress at work was measured by the effort-reward imbalance questionnaire. Perceived parental support was assessed by an item on parental empathy and their willingness to communicate with the adolescent. Suicidal ideation was considered positive if students reported thoughts about suicide every month or more frequently during the previous 6 months. Logistic regression was used to examine the associations. Results: We observed that parents' work stress was positively associated with low parental support, which was in turn associated with adolescent suicidal ideation. The odds ratio for parents' work stress and adolescent suicidal ideation was 2.91 (95% confidence interval: 1.53-5.53), and this association was markedly attenuated to 2.24 (95% confidence interval: 1.15-4.36) after additional adjustment for parental support. Notably, mothers' work stress levels exerted stronger effects on children's suicidal ideation than those of fathers. Conclusion: Parents' work stress (particularly mother's work stress) was strongly associated with adolescent's suicidal ideation, and the association was partially mediated by low parental support. These results need to be replicated and extended in prospective investigations within and beyond China, in order to explore potential causal pathways as a basis of preventive action.

• Strategy21
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• s.38
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• pp.112-162
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• 2015

This study began to confirm or review the balance of power theory by applying scientific methods through experiential cases. Though there are several kinds of national power, this study supposes military power as a crucial power when it comes to war and peace. This research covered balance and imbalance through comparing relative military power between nations or nations' group. Comparison of relative military power can be achieved by statistically processing the values of which has been converted into the standard variables in same domain, then calculating the values of nation's power which has been synthesized different experiential factors. In addition, the criteria of experiential experiment is highly dedicated to European countries, USA, Japan prior to 1st and 2nd World War, as well as USA, Soviet Union and North East Asia during Cold War era. In addition, the balance of power theory has been redefined to review the action of the state upon the changes of power as mentioned in the theory. To begin with, the redefined theory states that relative level of military power between nations defines the consistency of peace and balance of power. If military power is enough to be on the range of level required to keep the power in equilibrium, peace and balance can be achieved. The opposite would unbalance the military power, causing conflicts. While the relative military level between nations change, nations seek to establish 'nations group' via military cooperation such as alliance, which also shift relative military power between nations group as well. Thus, in order to achieve balance of power, a nation seeks to strengthen its military power(self-help), while pursuing military cooperation(or alliance). This changes relative military power between nations group also. In other words, if there exists balance of power between nations, there is balance of power between nations group as well. In this theory, WWI and II broke out due to the imbalance of military force between nations and nations group, and reviewed that due to the balance of military force during the Cold War, peace was maintained. WWI was resulted from imbalance of military cooperation between two powerful states group and WWII was occurred because of the imbalance among the states. Peace was maintained from cooperation of military power and balance among the states during the Cold War. Imbalance among continental states is more threatening than maritime states and balance of power made by army force and naval force also is feasible. Also the outcomes of two variables are found military power balanced ratio of military power for balance is 67% when variable ratio of balance is 100% and standard value for balance is 0.86. Military power exists in a form of range. The range is what unstabilized the international system causing nations to supplement their military powers. These results made possible the calculation and comparison between state's military power. How balance of power inflicted war and peace has been studied through scientific reviews. Military conflict is highly possible upon already unbalanced military powers of North East Asian countries, if the US draws its power back to America. China and Japan are constantly building up their military force. On the other hand, Korean military force is inferior so in accordance to change of international situation state's survival could be threatened and it is difficult to achieve drastic increase in military force like Germany did. Especially constructing naval force demands lots of time; however but has benefit that naval force can overcome imbalance between continental states and maritime states.

• Journal of Intelligence and Information Systems
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• v.28 no.4
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• pp.157-177
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• 2022

Investors are trading stocks by keeping a close watch on the order information submitted by domestic and foreign investors in real time through Limit Order Book information, so-called price current provided by securities firms. Will order information released in the Limit Order Book be useful in stock price prediction? This study analyzes whether it is significant as a predictor of future stock price up or down when order imbalances appear as investors' buying and selling orders are concentrated to one side during intra-day trading time. Using classification algorithms, this study improved the prediction accuracy of the order imbalance information on the short-term price up and down trend, that is the closing price up and down of the day. Day trading strategies are proposed using the predicted price trends of the classification algorithms and the trading performances are analyzed through empirical analysis. The 5-minute KOSPI200 Index Futures data were analyzed for 4,564 days from January 19, 2004 to June 30, 2022. The results of the empirical analysis are as follows. First, order imbalance information has a significant impact on the current stock prices. Second, the order imbalance information observed in the early morning has a significant forecasting power on the price trends from the early morning to the market closing time. Third, the Support Vector Machines algorithm showed the highest prediction accuracy on the day's closing price trends using the order imbalance information at 54.1%. Fourth, the order imbalance information measured at an early time of day had higher prediction accuracy than the order imbalance information measured at a later time of day. Fifth, the trading performances of the day trading strategies using the prediction results of the classification algorithms on the price up and down trends were higher than that of the benchmark trading strategy. Sixth, except for the K-Nearest Neighbor algorithm, all investment performances using the classification algorithms showed average higher total profits than that of the benchmark strategy. Seventh, the trading performances using the predictive results of the Logical Regression, Random Forest, Support Vector Machines, and XGBoost algorithms showed higher results than the benchmark strategy in the Sharpe Ratio, which evaluates both profitability and risk. This study has an academic difference from existing studies in that it documented the economic value of the total buy & sell order volume information among the Limit Order Book information. The empirical results of this study are also valuable to the market participants from a trading perspective. In future studies, it is necessary to improve the performance of the trading strategy using more accurate price prediction results by expanding to deep learning models which are actively being studied for predicting stock prices recently.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.13 no.11
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• pp.5594-5615
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• 2019

Malicious social robots, which are disseminators of malicious information on social networks, seriously affect information security and network environments. The detection of malicious social robots is a hot topic and a significant concern for researchers. A method based on classification has been widely used for social robot detection. However, this method of classification is limited by an unbalanced data set in which legitimate, negative samples outnumber malicious robots (positive samples), which leads to unsatisfactory detection results. This paper proposes the use of generative adversarial networks (GANs) to extend the unbalanced data sets before training classifiers to improve the detection of social robots. Five popular oversampling algorithms were compared in the experiments, and the effects of imbalance degree and the expansion ratio of the original data on oversampling were studied. The experimental results showed that the proposed method achieved better detection performance compared with other algorithms in terms of the F1 measure. The GAN method also performed well when the imbalance degree was smaller than 15%.

• Journal of Technology Innovation
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• v.16 no.2
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• pp.201-223
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• 2008

This paper studies the supply and demand of Industrial Technology Labor-force(ITL) and analyzes the determinate of ITL shortage in Korean manufacturing. We classified the industry into four categories-high technology industries, medium-high technology industries, medium-low technology industries and low technology industries-based on its R&D intensity like OECD. For the empirical analyses we use a survey data collected from 5,703 enterprises. The key findings are as follows: Firstly, a large majority of ITL is engaged in more technology-intensive industries but the categories that are exposed to more serious labor-force shortage problem are medium-high technology industries and low technology industries. Secondly, in the terms of supply factor, the ITL shortage problems are mainly due to the avoidance of ITL jobs. And the demand point, the reason is that the most of ITL are not researchers but production managers. Thirdly, the cause of imbalance between supply and demand of ITL are different by the technological categories. For example, in the high technology industries, the supply factors, such as average wage and turnover rate played more important role in the imbalance. But in the low technology industries the demand factors, such as per capita sales and the ratio of ITL in all employees were relatively much more important. Based on the findings, we discovered some political meanings such as the necessity to plan various policies to resolve the shortage problem of ITL according to the technological categories, etc.

• Journal of the Korean Society for Precision Engineering
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• v.28 no.10
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• pp.1159-1165
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• 2011

The recording density of HDD is increasing in ratio of 100% each year. Because the increasing of recording density requires the feature of high rotation, fixation and low-noise, fluid hydrodynamic bearing(FDB) has been paid attention to overcome a limitation in ball bearing. Most of researches related to improving performance of FDB have been studied in Japan which has 80% more market share of HDD spindle motor assembly. Main subject of studies are about for the design of the groove shape, manufacturing process of fluid dynamic bearing, performance evaluation and measurement. In HDD, non-repeatable runout(NRRO) is most important parameter which determines the performance of HDD spindle system because NRRO is unpredictable that cannot be compensated in head/slider servo system. In this study, performance evaluation system can measure dynamic behaviors were designed and methodology for calculating imbalance, RRO, and NRRO were proposed.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.11 no.9
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• pp.454-461
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• 2001

Acoustic noise and vibration of a BLDC motor is a coupled phenomenon between mechanical characteristics and electromagnetic origins through the motor air-gap. When a relative misalignment of rotor in the air-gap center exists on the assemblage, it is considered to influence the motor system characteristics. In this paper, the back electro motive force(BEMF) is analyzed by Finite Element Method(FEM) and verified by experiments for the SPM and IPM type motors. For magnetic field analysis, a FEM is used to account for the magnetic saturation. Using these results, the FEM is made to determine the appropriate electromagnetic field analysis in BLDC motors with rotor eccentricity ratio. A radial magnetic imbalance force of BLDC motor with rotor eccentricity is analyzed. Results demonstrate that the imbalance force is increased according to the degree of misalignment. An IPM motor, mostly chosen to realize high-speed operation, shows a worse effect on magnetic unbalanced forces and dynamic responses compared with SPM motor due to magnetic saturation when the rotor eccentricity exists.