• Publications of The Korean Astronomical Society
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• v.19 no.1
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• pp.101-107
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• 2004

This paper describes the digital back-end system for getting the data to analyze the user observation mode by digitalize the analog data after receiving the space radio using the radio telescope, The received analog data will be digitalized by high-speed sampler with 1 Gsps for 4 channel frequency band of millimeter wave, and the digital data will be transported through the fiber-optic digital transmission system and WDM(wavelength division multiplex) to observation building, The wideband digital FIR(Finite Impulse Response) filters analyze the data for user observation mode to record the data in high-speed recorder with 1 Gbps. In this paper, we introduce the overall system configuration and features combined by various information and communication technology in radio astronomy briefly, which will be adopted by KVN(Korean VLBI Network).

• Korean Journal of Childcare and Education
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• v.16 no.2
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• pp.25-45
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• 2020

Objective: The purpose of this study is to explore daycare-center director's perceptons of recruitment and to understand how hire beginning teachers. Methods: One hundred twenty-five directors of daycare-centers in Seoul, Incheon, and Gyeonggi-do Province answered a questionnaire that was developed by researchers. The results were analyzed by frequency analysis, descriptive statistics and multiple response analysis through SPSS 18.0. Furthermore, 17 of the directors that participated in the study were given individual interviews by qualitative methods for research. Results: First, 56.8% of the directors felt difficulty to employ beginning teachers because of 'lack of information about them' and 'uncertainty of practice capability.' On the other hand, other directors of daycare-centers said that they hire them for 'high acceptance' and 'operational efficiency of the daycare-center.' Second, the main way to recruit teachers for daycare-centers is open recruitment, and through recommendations of acquaintances or through colleges in relevant fields. Professional talent and personal characteristics were important selection criteria for recruitment, and daycare-center directors used interviews, résumés, cover-letters, and demo classes for the hiring process. Primarily, most directors select candidates through résumés and cover-letters, and the final selection is completed by conducting interviews. Conclusion/Implications: In conclusion, this study can be useful to prepare beginning teachers for employment and for educating applicants.

• Journal of Institute of Control, Robotics and Systems
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• v.4 no.6
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• pp.713-721
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• 1998

In this paper a new modeling and an optimal pole-placement control for the suspension system of Macpherson type are investigated. The rotational motion of the unsprung mass is emphasized in the new modeling. The two generalized coordinates selected in the new model are the vortical displacement of sprung mass and the angular displacement of control arm. Both variables are measured from their static equilibrium points. It is shown that the conventional model is a special case of the new model since the transfer function of the new model coincides with that of the conventional one if the lower support point of the shock absorber is located at the mass center of the unsprung mass. It is also shown that the resonance frequencies of the new model agree better with experimental results. Therefore, the new model is more general in the sense that it Provides an extra degree of freedom in determining the plant model for control system design. An optimal pole-placement control which combines LQ control and pole-placement technique is applied to the new model. Simulations are provided.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.46 no.3
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• pp.8-14
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• 2009

In this paper, it is proposed that the design of the PID controller with the internal model control structure for improved performance. Internal model was identification that is second-order plus dead time structure using final-value theorem and genetic algorithm The parameters of Controller are determined to minimize IAE(Integral of the Absolute value of the Error) and ITAE(Integral of the Time multiplied by the Absolute value of the Error) of performance index by internal model and numerical method. Simulation examples are given to show the better performance of the proposed method than conventional methods.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.44 no.1
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• pp.19-24
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• 2007

In this paper, we propose a tuning method of PID-PD controller to satisfy design specifications in frequency domain as well as time domain. The proposed tuning method of PID-PD controller consists of the convex set of PID and PI-PD controller. PID-PD controller controls the closed-loop response to be located between the step responses, and Bode magnitudes of closed-loop transfer functions controlled by PID and PI-PD controller. The controller is designed by the optimum tuning method to minimize the proposed specific cost function subject to sensor noise insensitivity and robust stability. Its effectiveness is examined by the case study and analysis.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.57 no.5
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• pp.845-851
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• 2008

A simple RMRAC (Robust Model Reference Adaptive Control) scheme for the PMSM (Permanent Magnent Synchronous Motor) is proposed in the synchronous frame. A current control of PMSM is the most inner loop of electro-mechanical driving systems and it requires a fast and simple control law to play a foundation role in the control hierarchy. In the proposed synchronous current model, the input signal is composed of a calculated voltage by proposed adaptive laws and real system disturbance. The gains of feed-forward and feedback controllers are estimated by the proposed modified Gradient method respectively, where the system disturbances are assumed as filtered current tracking errors. After the estimation of the system disturbances from the tracking errors, the corresponding voltage is fed forward to control input voltage to compensate for the disturbances. The proposed method is robust against high frequency disturbance and has a fast dynamic response. It also shows a good real-time performance due to it's simplicity of control structure. Through the simulations and real experiments, efficiency of the proposed method is verified.

• Journal of Electrical Engineering and Technology
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• v.10 no.3
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• pp.1304-1310
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• 2015

In remote islands, due to expense of existing generation systems, installation of photovoltaic cells (PVs) and wind turbines has a chance of reducing generation costs. However, in island power systems, even short-term power fluctuations change the frequency of grids because of their small inertia constant. In order to compensate power fluctuations, the authors proposed the power consumption control of pumps which send water to tanks. The power control doesn’t affect water users’ convenience as long as tanks hold water. Based on experimental characteristics of a pump system, this paper shows methods to determine reference power consumption of the system with compensation for short-term PV fluctuations while satisfying water demand. One method uses a PI controller and the other method calculates reference power consumption from water flow reference. Simulations with a PV and a pump system are carried out to find optimum parameters and to compare the methods. Results show that both PI control method and water flow calculation method are useful for satisfying the water demand constraint. The water demand constraint has a little impact to suppression of the short-term power fluctuation in this condition.

• Proceedings of the KIEE Conference
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• 2008.07a
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• pp.2299-2300
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• 2008

The Velocity Autocorrelation Function (VAF) of the sodium ions is calculated for a range of temperature from 250K to 1000K and converted into the linear ac-conductivity and ac-susceptibility response via Fourier transformation. A peak is found in the conductivity around $6{\times}10^{12}$ Hz that has some of the character of a Poley absorption. Here it is shown to be due to an harmonically coupled site vibrations of the sodium atoms, which extend only over a limited range. At frequencies below the peak the conductivity tends towards a constant i.e. dc value corresponding to a constant flow of ions through the simulation cell. At high temperatures the conductivity due to this ion transport process behaves like a metal with an insulator to metal transition occurring around a specific temperature.

• Proceedings of the KIEE Conference
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• 2008.07a
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• pp.924-925
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• 2008

There are many types of grid-connected inverter controllers, PI controller based is the most popular methods. But, a common PI control is produced zero-steady state error and phase delay in sinusoidal reference. Synchronous reference frame or DQ transform based controller is capable for reducing both of zero-steady state error and phase delay is. But DQ transform based controller has cross-coupling component which difficult to analyze the system in single phase model. In this paper, to obtained single phase model of the system, DQ transform based controller is analyzed in two techniques. The first is by neglecting cross-coupling. The second is eliminated cross-coupling component by decoupling method. By these two techniques, single phase model is obtained. Then, the single phase model is analyzed to evaluate its performance in stability and frequency response, through Root Locus and Bode diagram, respectively. MATLAB and PSIM simulation is used to verify the analysis. Simulation result is shown; cross-coupling component has no significant influent to the controller.

• Journal of the Korean Home Economics Association
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• v.45 no.6
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• pp.49-59
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• 2007

The purposes of this study were to determine the price elasticities of foodcourt-styled university foodservice, and to identify the attributes that affect these price elasticities. Questionnaires were distributed to 700 students at the K University in Masan, from September 21-27, 2006. 478 questionnaires were ultimately included in the final analysis(response rate: 68.3%). For statistical analysis, SPSS(12.0) was used to conduct the descriptive analysis, t-test, and ANOVA. The results of this study were as follows. The average meal price for in-campus foodservice was \ 2,196 and the average meal price for an off-campus restaurant was \3,044. The university students recognized that the proper price for in-campus foodservice and an off-campus restaurant were, respectively, \2,127 and \ 2,884. The price elasticities for foodcourt-styled university foodservice were 4.20(Kko-Bul-Kko-Bul), 3.83(Il-Poom-Hyang), and 4.10(Ne-Mo-Baek_Ban). The factors that affected price elasticity included the frequency of visiting foodservice, foodservice satisfaction, price satisfaction, and customer's responses to increased meal prices. The recommended price strategy for foodcourt-styled university foodservice was to lower meal price, which would attract more students and increase the sales volume. Simultaneously, foodservice managers should attempt to improve and increase customer satisfaction and the customer's perceived value for meal price. Overall, price elasticity may prove helpful in predicting the customer's behaviors on price changes, and may provide useful basic data for foodservice managers when establishing price strategy.