• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.18 no.3
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• pp.299-306
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• 2008

The electromagnet in Maglev vehicles controls the voltage in its winding to maintain the air gap, a clearance between the electromagnet and guideway, within an allowable deviation, with strongly interacting with the flexible guideway. Thus, the vibration characteristics of guideway plays important role in dynamics of Maglev vehicles using electromagnet as an active suspension system. The effects of the guideway's vibrational characteristics on dynamics of the Maglev vehicle UTM-01 are analyzed. The coupled equations of motion of the vehicle/guideway with 3 DOFs are derived. Eigenvalues are calculated and frequency response analysis is also performed for a clear understanding of the dynamic characteristics due to guideway vibration characteristics. To verify the results, tests of the urban Mgalev vehicle UTM-02 are carried out. It is recommended that the natural frequency of the guideway be minimized and its damping ratio in the Maglev vehicle with a 5-states feedback control law as a levitation control law.

• KOREAN JOURNAL OF PACKAGING SCIENCE & TECHNOLOGY
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• v.12 no.1
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• pp.35-40
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• 2006

Cushioning systems, which are cushion material and its designed configuration, are important to protect fragile items since they act as buffers between the impact force and the fragile product. As cushioning materials, several plastic foams are commonly used in industry. However, the utilization of the plastic material has been causing a solid waste problem and pollution. Thus, as an alternative cushion material to the plastic foams, a corrugated cushion, which is considered environmentally friendly and cheap material, was put into drop tests and its impact shock attenuation was investigated. Flat and free drop data were recorded and compared to the dynamic shock of EPS cushion. In addition, the mathematical model of the shock attenuation of the corrugated cushion was developed. The result showed that the corrugated cushion gave an excellent protection for items that were subjected to the limited number of drops. There was no significant difference of the shock absorbing ability between the EPS and corrugated cushions. Energy density model of cushioning material successfully explained the mechanical behavior and fatigue of the corrugated cushions.

• The Korean Journal of Applied Statistics
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• v.24 no.1
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• pp.1-10
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• 2011

This study investigates the dynamic structure of interdependence on the domestic and related major stock markets by employing a statistical framework. Finance theory predicts potential gains by international portfolio diversification if returns from investment in different national stock markets are not perfectly correlated or not cointegrated. The benefit of international diversification is limited when national stock markets are cointegrated because of the limited amount of independent variation by the presence of common factors. The statistical tests suggest that international diversification appears to be favorable after the period of the comovement of the stock prices caused by 1997 Asian financial crisis. The result reflects the increase in overseas investment and purchase of overseas funds after the early 2000's.

• Journal of Electrical Engineering and Technology
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• v.6 no.4
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• pp.439-446
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• 2011

Frequency is an important operating parameter for the protection, control, and stability of a power system. Thus, it must be maintained very close to its nominal frequency. Due to the sudden change in generation and loads or faults in a power system, however, frequency deviates from its nominal value. An accurate monitoring of the power frequency is essential for optimum operation and prevention of wide area blackout. Most conventional frequency estimation schemes are based on the DFT filter. In these schemes, the gain error could cause defects when the frequency deviates from the nominal value. We present an advanced frequency estimation technique using gain compensation to enhance the DFT filter-based technique. The proposed technique can reduce the gain error caused when the frequency deviates from the nominal value. Simulation studies are performed using both the data from EMTP-RV software and the user-defined arbitrary signals to demonstrate the effectiveness of the proposed algorithm. Results show that the proposed algorithm achieves good performance under both steady state tests and dynamic conditions.

• Journal of Electrical Engineering and Technology
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• v.6 no.2
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• pp.154-160
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• 2011

A new algorithm for estimating the fundamental frequency of power system signals is presented. The proposed algorithm consists of two stages: orthogonal decomposition and a complex Prony analysis. First, the input signal is decomposed into two orthogonal components using cosine and sine filters, and a variable window is adapted to enhance the performance of eliminating harmonics. Then a complex Prony analysis that is proposed in this paper is used to estimate the fundamental frequency by approximating the cosine-filtered and sine-filtered signals simultaneously. To evaluate the performance of the algorithm, amplitude modulation and harmonic tests were performed using simulated test signals. The performance of the algorithm was also assessed for dynamic conditions on a single-machine power system. The Electromagnetic Transients Program was used to generate voltage signals for a load increase and single phase-to-ground faults. The performance evaluation showed that the proposed algorithm accurately estimated the fundamental frequency of power system signals in the presence of amplitude modulation and harmonics.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.5
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• pp.2511-2515
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• 2013

Carbon black from pyrolysis of waste tires was used to modify and improve the fatigue properties and low temperature cracking of asphalt binder. 0%, 5%, 10%, 15% and 20% of pyrolyzed carbon black was mixed. Couple of laboratory tests, such as dynamic shear rheometer test and bending beam rheometer test, were carried out. The use of pyrolyzed carbon black decreased the fatigue at room temperature and improved the resistance of low temperature cracking up to $-12^{\circ}C$, but, was off the criteria at $-18^{\circ}C$.

• Journal of Labour Economics
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• v.34 no.3
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• pp.1-28
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• 2011

This paper empirically tests the theory that labor demand elasticity of unionized firms would be smaller than that of nonunionized firms, using the Korean firms' panel data for 1990-2009. The major findings are the following: First, the estimates of labor demand elasticity of unionized firms are in the range of 0.34-0.49, less than a half of those of nonunionized firms, hence supporting the theory. Second, the unionized firms are more rigid in dynamic adjustment of employment than nonunionized firms. Finally, there are no significant differences between unionized and nonunionized firms in the elasticity of substitution.

• The Journal of Korean Physical Therapy
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• v.28 no.4
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• pp.243-248
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• 2016

Purpose: This study was conducted to identify the effects of neuromuscular training performed on badminton club members' to improve muscle activity of the lower extremities and static and dynamic balance tests. Methods: The subjects were 20 badminton club members with chronic ankle instability who were randomly divided into a neuromuscular training group and a balance training group, each with 10 patients. Both exercises ware performed three days per week for 30 minutes a day over six weeks. Results: The neuromuscular training group showed increased muscle activity of the lower extremities compared to the balance training group. Neuromuscular training increased balance ability better than the balance training group, showing a significant difference and better efficiency of neuromuscular training when compared to balance training. Conclusion: This research evaluated neuromuscular training as an intervention for badminton club members with chronic ankle instability and compared the differences in muscle activity of the lower extremities and balance ability; as a result of the effective frequency for improving performance, there was a significant difference in muscle activity of lower extremities and balance ability of the neuromuscular training group and the control group.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.59 no.2
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• pp.173-178
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• 2010

Frequency is an important operating parameter of a power system. Due to the sudden change in generation and loads or faults in power system, the frequency is supposed to deviate from its nominal value. It is essential that the frequency of a power system be maintained very close to its nominal frequency. And monitoring and an accurate estimation of the power frequency by timing synchronized signal provided by FDR is essential to optimum operation and prevention for wide area blackout. As most conventional frequency estimation schemes are based on DFT filter, it has been pointed out that the gain error by change in magnitude could cause the defects when the power frequency is deviated from nominal value. In this paper, an advanced frequency estimation scheme using gain compensation for fault disturbance recorders (FDR) is presented. The proposed scheme can reduce the gain error caused when the power frequency is deviated from nominal value. Various simulation using both the data from EMTP package and user's defined arbitrary signals are performed to demonstrate the effectiveness of the proposed scheme. The simulation results show that the proposed scheme can provide better accuracy and higher robustness to harmonics and noise under both steady state tests and dynamic conditions.

• Journal of Electrical Engineering and Technology
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• v.8 no.6
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• pp.1431-1438
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• 2013

A pack-level battery hardware-in-the-loop simulation (B-HILS) platform is implemented. It consists of dynamic vehicle models using PSAT and multiple control interfaces including real-time 3D driving and GPS mode. In real-time 3D driving mode, user can drive a virtual vehicle using actual drive equipment such as steering wheel and accelerator to generate the cycle profile of the battery. In GPS mode, actual road traffic and terrain effects can be simulated using GPS data while the trajectory is displayed on Google map. In the latter part of the paper, several performance tests of an actual lithium-polymer battery pack are carried out utilizing the developed system. All experiments are conducted as parts of actual development process of a commercial battery pack adopting 2nd generation Prius as a target vehicle model. Through the experiments, the low temperature performance and fuel efficiency of the battery are quantitatively investigated in comparison with the original nickel-metal hydride (NiMH) pack of the Prius.