• Journal of the Korean Institute of Intelligent Systems
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• v.22 no.1
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• pp.56-61
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• 2012

This paper propose the robust stability algorithm for controlling a variable speed wind power system which based on doubly-fed induction generator (DFIG). The control object in the wind power system enables the rotor to rotate without any physical contact by using magnetic force. Generally, the system dynamics of the wind power system has severe nonlinearity and uncertainty so that it is not easy to obtain the control objective. For solving these problems, we propose the fuzzy modelling and robust control algorithm for wind power system. The sufficient conditions for robust controller are obtained in terms of solutions to linear matrix inequalities (LMIs). Simulation results for wind power system based on DFIG are demonstrated to visualize the feasibility of the proposed method.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.49 no.2
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• pp.10-16
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• 2012

Currently, the majority of systems which are non-linear are in need of the correct system equations for controlling and monitoring. Therefore, the correct estimation of parameters is crucial. Generally, parameters are changed due to system deterioration or sudden environmental alterations. Given the limitations of system monitoring unstable controls can arise. In the following paper, the parameter estimation method is proposed using software filters to combat these system instabilities. For dynamic instances, a powerful particle filter is used to control the nonlinear and noisy environments in which they take place. Using a setup simulation comprised of a slider and pendulum, the state variable of noise is obtained. After collecting the data, the proposed algorithm is used to estimate both the state variable and its parameters. Finally, these results are checked with correct parameter estimations to evaluate and verify the algorithms performance.

• Journal of Preventive Medicine and Public Health
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• v.47 no.3
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• pp.150-157
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• 2014

Objectives: The decrease or increase in sleep duration has recently been recognized as a risk factor for several diseases, including hypertension and obesity. Many studies have explored the relationship of decreased sleep durations and injuries, but few have examined the relationship between increased sleep duration and injury. The objective of this research is to identify the risk for injury associated with both decreased and increased sleep durations. Methods: Data from the 2010 Community Health Survey were used in this study. We conducted logistic regression with average sleep duration as the independent variable, injury as a dependent variable, and controlling for age, sex, occupation, education, region (cities and provinces), smoking, alcohol use, body mass index, hypertension, diabetes, arthritis, and depression. Seven categories of sleep duration were established: ${\leq}4$, 5, 6, 7, 8, 9, and ${\geq}10$ hours. Results: Using 7 hours of sleep as the reference, the adjusted injury risk (odds ratio) for those sleeping a total of ${\leq}4$ h/d was 1.53; 1.28 for 5 hours, for 1.11 for 6 hours, 0.98 for 8 hours, 1.12 for 9 hours, and 1.48 for ${\geq}10$ hours. The difference in risk was statistically significant for each category except for the 8 and 9 hours. In this study, risk increased as the sleep duration decreased or increased, except for the 8 and 9 hours. Conclusions: This research found that either a decrease or increase in sleep duration was associated with an increased risk for injury. The concept of proper sleep duration can be evaluated by its associated injury risk.

• KIISE Transactions on Computing Practices
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• v.22 no.9
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• pp.405-418
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• 2016

Recently, many researchers have studied the VSL decision method using traffic information in multiple detector zones. However, this method selects incorrect VSL starting points, leading to the selection of the wrong speed control zone and calculation of the wrong VSL, causing traffic congestion. Eventually, the Unstable VSL system causes more congestion on the freeway. This paper proposes an improved VSL algorithm stably operated in multiple detector zones on the Korea highway. The proposed algorithm selects a preliminary VSL start station (VSS) expected to end the congestion using the acceleration of stations. It also determines the VSS at each congestion area. Finally, it calculates the VSL relative to the determined VSS and controls the vehicles that enters the traffic congestion zone. The developed strategy is compared with Real-time Variable Speed Limits for Urban Freeway (RVSL) to test the stability and efficiency of the proposed algorithm. The results show that the proposed algorithm resolves the problems of the existing algorithm, demonstrated by the correct VSS decision and the reduction of total travel time by 1-2 minutes.

• Journal of the Institute of Convergence Signal Processing
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• v.12 no.4
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• pp.355-361
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• 2011

The power control of the existing heating element has been using the On-Off control, phase control, and PWM control. In case of controlling power PTC heating element developed recently with the existing method, the temperature is unable to be precisely controlled or the harmful electromagnetic wave to human body is generated. In this paper, We suggest the power control of PTC heating cable using variable AC Cycles. This regards the AC cycle of N as the unit of the power control. It determines On-Off for each cycle. It is the AC power control method in which it arranges the on-cycle in N cycles in the random and it supplies the current continuously. At this time. the minimal electric power amount becomes 1/N. The maximum current amount becomes 1 and sets up the number of on cycles according to the set value and can control the electric power with the step of N consistently. In the PTC heating system, we show that proposed power control method is superior in the EMI and temperature control property using MATLAB simulation, experiments and measurements.

• The Journal of Industrial Distribution & Business
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• v.9 no.6
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• pp.49-55
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• 2018

Purpose - This paper examines the effect of related party transactions on crash firm-specific stock price crash risk. Ownership of a typical Korean conglomerate is concentrated in a single family. In those entities, management and board positions are often filled by family members. Therefore, a dominant shareholder can benefit from related party transactions. In Korea, firms have to report related party transactions in financial statement footnotes. However, those are not disclosed in detail. The more related party transactions are the greater information risk. Thus, companies with related party transactions are likely to experience stock price crashes. Research design, data, and methodology - 2,598 firm-year observations are used for the main analysis. Those samples are from TS2000 database from 2009 to 2013, and the database covers KOSPI-listed firms in Korea. The proxy for related party transactions (RTP) is calculated by dividing total transactions to the related-party by total sales. A dummy variable is used as a dependent variable (CRASH) in the regression model. Logistic regression is used to explain the relationship between related party transactions and crash risk. Then, the sample was separated into two groups; tunneling firms and propping firms. The relation between related party transactions and crash risk variances with features of the transaction were investigated. Results - Using a sample of KOSPI-listed firms in TS2000 database for the period of 2009-2013, I find that stock price crash risk increases as the trade volume of related-party transactions increases. Specifically, I find that the coefficient of RPT is significantly positive, supporting the prediction. In addition, this relationship is strong and robust in tunneling firms. Conclusions - The results report that firms with related party transactions are more likely to experience stock price crashes. The results mean that related party transactions increase the possibility of future stock price crashes by enlarging information asymmetry between controlling shareholders and minority shareholders. In case of tunneling, it could be seen that related party transactions are positively associated with stock crash risk. The result implies that the characteristic of the transaction influences crash risk. This study is related to a literature that investigates the effect of related party transactions on the stock market.

• Korea Journal of Hospital Management
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• v.22 no.2
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• pp.58-69
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• 2017

Recently, with the increase in the number of private health insurance subscribers, interest in overuse of the medical service is increasing. This study analyzed the impacts of private health insurance (PHI) on medical institution selection in outpatient service utilization among persons with arthritis. In order to control patients' health status, we extracted outpatient episodes with the same disease (KCD6, M13) from Korea Health Panel. The unit of analysis was an outpatient visit with arthritis in 2014 (n=23,363). In the light of insurance coverage, we redefined three type of private health insurance (ex, indemnity, fixed benefit, and non-insured) as a test variable and two type of medical institution (ex, hospital and physician visit) as a dependent variable. We conducted a probit regression analysis to identify the impacts of PHI on medical institution selection controlling for heteroscedasticity. The results of this study showed that the insured with indemnity were more likely to choose hospital departments than clinics (marginal effect=0.0475, p=0.000). The impact of participation of fixed benefit PHI was not as clear as that of indemnity type (marginal effect=0.0162, p=0.047). In conclusion, this study confirmed that PHI, particularly indemnity type has a significant impact on the selection of medical institutions. Healthcare policy makers should consider that PHI not only affects the overall quantitative increase in healthcare utilization, but also influences the selection of medical institutions.

• Journal of Family Resource Management and Policy Review
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• v.20 no.3
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• pp.1-23
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• 2016

This study analyzes the effects of caring for grandchildren on Korean grandparents' health, using the Korean Longitudinal Study of Aging from 2006 to 2012. We investigate how caregiving is provided and analyze the effects of caregiving on grandparents' physical health, mental health, and health-related behaviors. As elderly people's health is generally frail, it is unclear whether the provision of childcare affects their health negatively. We control for the endogeneity of caregiving by an individual fixed effect (FE) model and instrumental variable-fixed effect (FE-IV) models. Using these models, we determine the endogeneity of caregiving and show that the significant effects of caregiving on health disappear as we control for endogeneity in the FE and FE-IV models. Even after controlling for endogeneity, we find that caregiving increases the probability of feeling pain as well as the number of different types of pain. Furthermore, caregiving increases the probability of restrictions on daily activities because of pain. On the other hand, caregiving reduces the symptoms of depression. In relation to health-related behaviors, caregiving reduces the probability of physical exercise and regular meals. Our results imply that although caregiving has a positive effect on mental health, the increase in physical pain and in non-healthy behaviors may lead to a deterioration of the caregiver's long-term health, which in turn may increase the medical costs of the elderly. Potential policy alternatives are discussed in the paper.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.44 no.7 s.361
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• pp.54-61
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• 2007

A variable gain low noise amplifier (VG-LNA) implemented in TSMC 0.18 um process is presented. This VG-LNA is designed of two stage amplifier, and its gain is controlled by the shunt feedback loop composed of a gain control transistor (GCT) and a coupling capacitor in second stage. The channel resistance of GCT in the shunt feedback loop influences the input and output stages of a second stage by the Miller effect. Total gain of the proposed VG-LNA is changed by two factors, the load impedance reduction and the interstage mismatch by controlling the channel resistance of the GCT. Consequently, by adding a shunt feedback with a gain control transistor, this proposed VG-LNA achieves both wide gain tuning range of 37 dB and continuous gain control simultaneously.

• The Journal of Korean Society for School & Community Health Education
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• v.20 no.2
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• pp.37-51
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• 2019

Purpose: This study aims to substantiate a correlation between the period of living alone in a shabby one-room and a depression experience. Methods: We conducted a cross-sectional study using data from the Korea Homeless Survey carried out by the Korea Institute for Health and Social Affairs in 2016. In the study, the data included 485 survey participants who resided in a single room. The period of single-room occupancy being divided into three groups: less than 1 year, 1 to 4 years, and more than 5 years was considered a primary independent variable. The outcome variable which represented a depression experience was measured by CESD-11(The Center for Epidemiological Studies-Depression Scale). We carried out a Chi-square test and multiple logistic regression to evaluate the association. Results: The rate of depression experienced in this population was 77.5%. Almost 83.9% of the participants were reported as being unable to receive the mental health counselling in the last 12 months. After controlling for covariates, subjects who were living in a single room occupancy for 1-5 years(OR=3.89; 95% CI=1.43-10.56) and more than 5 years(OR=2.71; 95% CI= 1.05-6.95) were found to be more likely to experience depression. Conclusions: The results showed that living alone in a shabby one-room had a high correlation with experiencing depression. We proposed that there is a need to develop a new strategy for mental health promotion program for the poor, vulnerable and deprived population.