• Transactions of the Korean Society of Automotive Engineers
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• v.7 no.7
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• pp.250-257
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• 1999

Driving simulators are used effectively for human factor study, vehicle system development and other purposes by enabling to reproduce actural driving conditions in a safe and tightly controlled enviornment. Interactive simulation requries appropriate sensory and stimulus cuing to the driver . Sensory and stimulus feedback can include visual , auditory, motion, and proprioceptive cues. A fixed-base driving simulator has been developed in this study for vehicle system developmnet and human factor study . The simulator consists of improved and synergistic subsystems (a real-time vehicle simulation system, a visual/audio system and a control force loading system) based on the motion -base simulator, KMU DS-Ⅰ developed for design and evaluation of a full-scale driving simulator and for driver-vehicle interaction.

• Journal of Power Electronics
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• v.15 no.1
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• pp.78-85
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• 2015

This paper presents a new structure of single-stage flyback power factor correction (PFC) converter with a controllable coupled negative magnetic feedback (NMF) winding. NMF winding is used to reduce the bulk capacitor voltage at high line voltages and light loads. However, it would cause line current distortion at zero crossing condition. In the proposed circuit, a series winding is used with NMF inductor to eliminate the NMF inductor at low line voltages. As a result, the dead angle of the input current, near zero voltage crossing, is eliminated and the power factor is increased. The presented experimental results of the proposed PFC converter confirm the integrity of the new idea and the theoretical analysis.

• Journal of Power Electronics
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• v.14 no.4
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• pp.712-721
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• 2014

This paper introduces a simple grid-voltage-sensorless control scheme for single-phase power factor correction (PFC) boost converters. The grid voltage waveform is obtained based on the dc output voltage, the switching duty ratio, and a phase-lead compensator. In addition, the duty ratio feedback is utilized to obtain the unity input power factor and the zero harmonic current. The proposed control scheme is designed and mathematically analyzed based on a small-signal model of PFC boost converters. To verify the effectiveness of the proposed control scheme, several simulations and experiments are carried out in two applications: an industrial power system with a 60 Hz grid frequency and a commercial aircraft application with a 400 Hz grid frequency.

• Proceedings of the KIEE Conference
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• 2005.07c
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• pp.1954-1956
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• 2005

본 논문에서는 SMPS(Switch-Mode Power Supply)의 역률을 개선할 수 있는 power factor correction(PFC) IC를 설계하였다. 설계된 PFC IC에는 전원장치의 power MOSFET을 구동할 수 있는 기능 이외에도 과전압, 과전류 및 단락보호 기능이 포함되어 있다. 또한 시스템이 대기상태에 있는 경우, 전압 및 전류 feedback 제어에 의해 효과적으로 대기전력을 절감할 수 있도록 설계하였다. 설계된 PFC IC는 시스템이 대기상태에서 일정시간동안 부하변동이 없을 경우 이를 감지하여 자동으로 시스템을 off 시켜 대기전력 소모를 최소화 하는 기능을 포함하고 있다.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.46 no.6
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• pp.48-55
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• 2009

The feedback interference channels are those made through the multipaths that are built by moving and stationary objects around transmit and receive antennas mounted at the same point. This paper describes the method to measure the feedback interference channels in the rural regions and sides of highways and the analysis on channel characteristic parameters. Using the measured samples, we estimated scattering functions, delay power spectra, and Doppler power spectra, and we analyzed the channels using eight parameters including coherence bandwidth, coherence time, maximum excess delay, average excess delay, rms delay spread, Doppler shift, Doppler spread, and spread factor, and delay and Doppler cumulative distributions. Even though many observations are made, note that the feedback signals of high Doppler frequencies and large energy are observed in the sides of highways due to high speed vehicles while low Doppler frequencies occurred in the rural region due to rare traffic.

• Journal of the Korean Society for Precision Engineering
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• v.13 no.10
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• pp.154-160
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• 1996

The control of diamond turning is usually achieved through a laser-interferometer feedback of slide position. The limitation of this control scheme is that the feedback signal does not account for additional dynamics of the tool post and the material removal process. If the tool post is rigid and the material removal process is relatively static, then such a non-collocated position feedback control scheme may surfice. However, as the accuracy requirement gets tighter and desired surface cnotours become more complex, the need for a direct tool-tip sensing becomes inevitable. The physical constraints of the machining process prohibit any reasonable implementation of a tool-tip motion measurement. It is proposed that the measured force normal to the face of the workpiece can be filtered through an appropriate admittance transfer function to result in the estimated dapth of cut. This can be compared to the desired depth of cut to generate the adjustment control action in additn to position feedback control. In this work, the design methodology on the admittance model-based control with a conventional controller is presented. The recursive least-squares algorithm with forgetting factor is proposed to identify the parameters and update the cutting process in real time. The normal cutting forces are measured to identify the cutting dynamics in the real diamond turning process using the precision dynamoneter. Based on the parameter estimation of cutting dynamics and the admitance model-based nanodynamic control scheme, simulation results are shown.

• Journal of Internet Computing and Services
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• v.10 no.3
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• pp.159-172
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• 2009

The purposes of this study were to identify factors affecting the quality of universities' e-learning contents from the perspectives of learners and to find out specific solutions for improving them. To achieve these goals, research questions were established as follows: 1) What factors were influencing the quality of universities' e-learning contents, and how were learners perceived about each factor(by its importance and satisfaction)? 2) Were there any differences on the learners' perceptions about each factor(by its importance and satisfaction)? 3) What were any specific ways to enhance the quality of universities' e-learning contents? The participants were of 543 university students who took at least one e-learning course and were living in the metropolitan areas(Seoul, Incheon, Gyeonggi). The survey questionnaire was consisted of 38 items developed through the literature review. To analyze the data collected, factor analysis and paired-sample t-test were conducted. The results were as follows: Five identified factors influencing the quality of universities' e-learning contents from the perspectives of learners were instructional strategies, learning contents, usability, evaluation/feedback, and interface design, and all identified factors were statistically significant differences among the learners' perceptions of its importance and satisfaction. The analysis results of importance-satisfaction matrix by each factor showed that 1) learning contents was the factor that current status should be at least continuously maintained, 2) usability, instructional strategies, and evaluation/feedback were the factors that learners' satisfactions still need to be increased although those importances were not relatively high, and 3) interface factor was important, while learners' satisfaction toward it was not much high so that solutions to increase the satisfaction need to be immediately considered. Based on the results, several suggestions to enhance universities' e-learning contents from the learners' perspectives were also recommended.

• The Transactions of the Korean Institute of Power Electronics
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• v.8 no.1
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• pp.70-79
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• 2003

In this paper, T5 28-watt fluorescent lamp ballast using a piezoelectric transformer is fabricated and its characteristic is investigated. Developed electronic ballast is composed of basic circuits and blocks, such as rectifier part, active power factor corrector part, frequency oscillation part using microcontroller and feedback control, piezoelectric transformer and resonant half bridge inverters. The fabricated ballast uses to variable frequency methode in external so exciting that the frequency of piezoelectric transformer could be generated by voltage control oscillator using microcontroller(AT90S4433). The current of fluorescent lamp is detected by feedback control circuit. The signal of inverter output is received using Piezoelectric transformer, and then its output transmitted to fluorescent lamp. Traditional electromagnetic ballasts operated at 50-60Hz have been suffered from noticeable flicker, high loss, large crest factor and heavy weight. A new electronic ballast is operated at high frequency about 75kHz, and then Input power factor, distortion of total harmonic and lamp current crest factor are measured about 0.9!35, 12H and 1.5, respectively Accordingly, the traditional ballast is by fabricated electronic ballast using piezoelectric transformer and voltage control oscillator because of its lighter weight, high efficiency, economic merit and saving energy.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.13 no.1
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• pp.35-41
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• 2020

Fast Fourier transform (FFT) processors have been widely used in various application such as communications, image, and biomedical signal processing. Especially, high-performance and low-power FFT processing is indispensable in OFDM-based communication systems. This paper presents a novel radix-26 FFT algorithm with low computational complexity and high hardware efficiency. Applying a 7-dimensional index mapping, the twiddle factor is decomposed and then radix-26 FFT algorithm is derived. The proposed algorithm has a simple twiddle factor sequence and a small number of complex multiplications, which can reduce the memory size for storing the twiddle factor. When the coefficient of twiddle factor is small, complex constant multipliers can be used efficiently instead of complex multipliers. Complex constant multipliers can be designed more efficiently using canonic signed digit (CSD) and common subexpression elimination (CSE) algorithm. An efficient complex constant multiplier design method for the twiddle factor multiplication used in the proposed radix-26 algorithm is proposed applying CSD and CSE algorithm. To evaluate performance of the previous and the proposed methods, 256-point single-path delay feedback (SDF) FFT is designed and synthesized into FPGA. The proposed algorithm uses about 10% less hardware than the previous algorithm.

• BMB Reports
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• v.29 no.6
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• pp.549-554
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• 1996

Phosphoinositide turnover in response to platelet-derived growth factor, epidermal growth factor, and bradykinin was evaluated in NIH 3T3 cells. Platelet-derived growth factor and bradykinin induced a significant increase in incorporation of $^{32}P$ into phosphatidylinositol (PI), phosphatidylinositol 4-monophosphate (PIP), and phosphatidylinositol 4.5-bisphosphate ($PIP_2$) in serum-starved NIH 3T3 cells. However, epidermal growth factor increased incorporation of $^{32}P$ into these phosphoinositides by only a small amount. Stimulation with platelet-derived growth factor, not bradykinin, caused a rapid elevation of PI and PIP kinase activities that were maximally activated within 10 min. The maximal levels of their elevation in cells with plateletderived growth factor stimulation were 3.2-fold for PI kinase, and 2.1-fold for PIP kinase. Short term pretreatment of NIH 3T3 cells with phorbol 12-myristate 13-acetate, activator of protein kinase C. caused an approximately 60% decrease in platelet-derived growth factor-induced PI kinase activities, indicating the feedback regulation of phosphoinositide turnover by protein kinase C. These results suggest that although the enhancement of phosphoinositide turnover is a rapidly occurring response in platelet-derived growth factor- or bradykinin-stimulated NIH 3T3 cells, phosphoinositide kinases may be associated with initial signal transduction pathway relevant to platelet-derived growth factor but not to bradykinin.