• 전기학회논문지
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• 제62권7호
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• pp.913-917
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• 2013

During the restoration process of primary restorative transmission system, some over voltages may happen due to nonlinear interaction between unloaded transformers and transmission systems. These over voltages caused by harmonic resonance can be suppressed by inserting damping loads before energizing transformers. But it is very difficult to predict the occurrence possibility of harmonic resonance and complex simulation must be repeated to estimate the sufficient damping loads. This paper presents a damping loads prediction system to prevent harmonic resonance. Detailed analysis of the relationship between harmonic resonance and the amount of damping loads is discussed. The prediction system is developed using a curve fitting and a neural network based on this relationship. A curve fitting used a Gaussian function based on non-linear least square method and multi-layer back-propagation neural network is applied. The system is applied to primary restorative transmission lines in korean power system and the result showed satisfactory performance.

• 동력기계공학회지
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• 제10권3호
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• pp.45-50
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• 2006

In this paper, creep tests of Mg-Zn-Mn and Mg-Zn-Mn-Ca alloy casted by mold under the temperature range of 473.00-573.00K, and the stress range of 23.42-87.00Mpa were done with the equipment of automatic controlled temperature and computer for data acquisition. The activation energies were obtained by relationship between creep rate and temperature, and the stress exponents were obtained by relationship between creep rate and stress. From the experiment results, the activation energies of Mg-Zn-Mn and Mg-Zn-Mn-Ca alloy were 149.87kJ/mol, 147.97kJ/mol, respectively, and the stress exponents of those alloy were 5.13, 5.59, respectively, under the temperature of 473.00-493.00K and the stress range of 62.43-78.00Mpa. And the activation energies of those alloy were 134.41kJ/mol, 129.22kJ/mol, respectively, and the stress exponent of those alloy were 3.48, 3.77, respectively, under the temperature of 553-573Mpa and the stress range of 23.42-39.00Mpa. Also the lifes of Mg-Zn-Mn-Ca alloy were higher than those of Mg-Zn-Mn alloy, and the results of SEM showed fracture surfaces under low temperature had smaller dimples than those under high temperature.

• 품질경영학회지
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• 제41권4호
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• pp.659-672
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• 2013

Purpose: The purpose of this study was to estimate life time of halogen lamps and acceleration factors using accelerated life test. Methods: Voltage was selected as an accelerating variable through the technical review about failure mechanism. The test was performed at 14.5V, 15.5V and 16.5 for 4,471 hours. It was assumed that the lifetime of Halogen lamps follow Weibull distribution and the inverse power life-stress relationship models. Results: Mean lifetimes of pin and screw types were 19,477 hours and 6,056 hours, respectively. In addition, acceleration factor of two items are calculated as 4.8 and 2.2 based on 15.5V, respectively. Conclusion: The life-stress relationship, acceleration factor, and MTTF at design condition are estimated by analyzing the accelerated life test data. These results suggest that voltage was very important factor to accelerate life time in the case of halogen lamps and the life time of pin type is three times longer than screw type lamps.

• Journal of Electrical Engineering and Technology
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• 제12권4호
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• pp.1471-1483
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• 2017

The low-frequency characteristics of four-switch three-phase (FSTP) inverter are investigated in this paper. Firstly, a general space vector pulse width modulation (SVPWM) directly involved the neutral point voltage of DC-link is proposed, where no sector identifications and trigonometric function calculations are needed. Subsequently, to suppress the DC offset in the neutral point voltage, the relationship between the neutral point voltage and the ${\beta}-axis$ component of the load current is derived, and then a new neutral point voltage control scheme is proposed where no low pass filter is adopted. Finally, the relationship between the load power factor and the maximum linear modulation index of the FSTP inverter is revealed. Since the operational region for the FSTP inverter in low frequency is reduced by the enlarged amplitude of the neutral point voltage, a linear modulation range enlargement scheme is proposed. A permanent magnet synchronous motor with preset rotary speed serves as the low-frequency load of the FSTP inverter. Experimental results verify that the new neutral point voltage control scheme is effective in the deviation suppression of the neutral point voltage, and the proposed scheme is able to provide a larger linear operational region in low frequency.

• 경영과정보연구
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• 제29권2호
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• pp.119-151
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• 2010

본 연구는 문화와 정서지능과의 의존관계를 정립하여 정서지능 연구에 새로운 시각을 부여하려고 했다. 본 연구의 전제는 개인정서의 지각, 평가, 표현, 이해, 조절 등이 문화에 크게 영향을 받기 때문에 인간의 다양한 정서 프로세스를 기초로 개발된 정서지능 역시 문화에 많은 영향을 받는다는 것이다. 본 논문은 문화가 정서지능에 미치는 영향을 규명하기 위해서 미국과 한국의 직장인을 대상으로 정서지능을 측정한 후, 정서지능과 문화의 의존관계를 실험하였다. 주어진 상황 아래서 정서적 반응이 문화 간 다양한 변화를 보인다는 것을 입증함으로서 정서지능이 문화에 의존한다는 것을 보였다. 또한, 본 연구는 Bar-On Emotional Quotient-Inventory (EQ-i)의 2차 데이터를 사용하여 13개국의 19,402명의 정서지능과 문화적 거리의 관계를 조사하였다. 연구결과로서 Hofstede의 문화차원 중 권력의 거리 (power distance)만이 정서지능에 유의미한 결과를 보였다.

• 척추신경추나의학회지
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• 제4권2호
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• pp.1-12
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• 2009

Objectives : The purpose of this study was to investigate the relationship between pain and psychological state in female office workers with neck pain. Methods : Experimental group of 31 healthy subjects complained of neck and arm discomfort related to computer use which lasted more than 3 months in the past year and was present in the past 7 days as well as on the day of test. Outcomes were assessed by meridian-electromyography(MEMG), Neck Disability Index(NDI), Visual Analog Scale(VAS), Beck Depression Inventory(BDI), Stress Reaction Inventory(SRI), Holmes & Rahe Social Readjustment Rating Scale(SRRS). Results : The NDI score and BDI score had a correlationship(r=0.48), and the NDI score and SRI score also had a correlationship(r=0.48), significantly. The NDI score and contraction power of upper trapezius by MEMG had a correlationship significantly, but with the other muscles the NDI score didn't have correlationships. The NDI score and the SRI score were significantly higher in depression group(BDI score ${\circ}{\surd}$14). The contraction power of trapezius by MEMG was significantly lower in depression group. Conclusions : The results suggest that mental stress can be a major risk factor of neck pain in female office workers.

• 성인간호학회지
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• 제29권1호
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• pp.87-97
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• 2017

Purpose: The purpose of this study was to investigate the relationship among sleep quality, heart rate variability (HRV), fatigue, depression, and anxiety reported by Korean adults. Methods: A cross-sectional study of 208 adults aged 20~60 years was conducted using a short-term HRV analysis and self-reported questionnaires of Pittsburgh Sleep Quality Index (PSQI), Fatigue Severity Scale, Beck Depression Inventory, and State Trait Anxiety Inventory. Results: Subjects with good sleep quality (PSQI $score{\leq}5$) had higher HRV total power (t=2.03, p=.043) and high-frequency (t=2.04, p=.043) with lower fatigue (t=-4.08, p<.001), depressive mood (t=-3.66, p<.001), and trait anxiety (t=-3.84, p<.001) than subjects with poor sleep quality. Poor sleep quality was negatively correlated with HRV total power (r=-.17, p=.016), high-frequency (r=-.14, p=.049), and positively fatigue (r=.39, p<.001), depression (r=.44, p<.001), state anxiety (r=.23, p=.001) and trait anxiety (r=.34, p<.001). Conclusion: The results indicated that sleep quality is correlated with HRV which reflects the activities of the autonomic nerve system, fatigue, depression, and anxiety in adults.

• 동력기계공학회지
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• 제17권2호
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• pp.114-120
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• 2013

This study was carried out to investigate the relationship between mechanical properties and damping capacity in high manganese austenitic stainless steel with two phase mixed structure of reversed austenite and deformation induced martensite. Reversed austenite of ultra-fine grain size less than $0.3{\mu}m$ was obtained by reversion treatment. Two phase structure of deformation induced martensite and reversed austenite was obtained by annealing treatment at range of $500^{\circ}C{\sim}700^{\circ}C$ for various time in cold rolled high manganese austenite stainless steel. In stainless steel with two phase mixed structure of martensite and austenite, damping capacity decreased rapidly with the increasing hardness and strength. With the increasing elongation, damping capacity was increased rapidly and then, slowly increased.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2008년도 제39회 하계학술대회
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• pp.103-104
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• 2008

This paper proposes an alternative methodology for deciding an optimum deterministic reliability level (IRR; Installed Reserve Rate) by using probabilistic reliability criterion (LOLE; Loss of Load Expectation). Additionally, case studies using the proposed method induce the characteristics of relationship between the probabilistic reliability index (LOLE) and deterministic reliability index (IRR) for 2008 year in Korea power system. The case study presents a possibility that an optimum IRR level in Korea can be assessed using the proposed method. Korea power system has been using the LOLE criterion to determine the adequacy of installed capacity (ICAP) requirement. The criterion in Korea is that the loss of load expectation shall not exceed the available capacity more than five day in ten years (=0.5[days/year]). The probabilistic reliability evaluation and production cost simulation program which is called PRASim is used in order to evaluate the relationship and optimum IRR in this paper.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2007년도 추계종합학술대회
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• pp.457-461
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• 2007

In many applications, received signal strength indicator is used for location tracking and sensor nodes localization. For location finding, the distances between sensor nodes can be estimated by converting received signal's power into distance using path loss prediction model. Many researches have done the analysis of power-distance relationship for radio channel characterization. In indoor environment, the general conclusion is the non-linear variation of RSSI values as distance varied linearly. This has been one of the difficulties for indoor localization. This paper presents works on indoor RSSI characterization based on statistical methods to find the overall trend of RSSI variation at different places and times within the same room From experiments, it has been shown that the variation of RSSI values can be determined by both spatial and temporal factors. This two factors are directly indicated by the two main parameters of path loss prediction model. The results show that all sensor nodes which are located at different places share the same characterization value for the temporal parameter whereas different values for the spatial parameters. Using this relationship, the characterization for location estimation can be more efficient and accurate.