• ETRI Journal
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• v.29 no.1
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• pp.89-94
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• 2007

A mathematical model for the input-output characteristic of an amplifier exhibiting gain expansion and weak and strong nonlinearities is presented. The model, basically a Fourier-series function, can yield closed-form series expressions for the amplitudes of the output components resulting from multisinusoidal input signals to the amplifier. The special case of an equal-amplitude two-tone input signal is considered in detail. The results show that unless the input signal can drive the amplifier into its nonlinear region, no gain expansion or minimum intermodulation performance can be achieved. For sufficiently large input amplitudes that can drive the amplifier into its nonlinear region, gain expansion and minimum intermodulation performance can be achieved. The input amplitudes at which these phenomena are observed are strongly dependent on the amplifier characteristics.

• International Journal of Human Ecology
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• v.10 no.1
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• pp.99-112
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• 2009

This study explored the consistency in service-learning courses through comparing course syllabi and faculty survey in order to incorporate a service-learning course into the Home Economics practicum. The first step was to examine how consistent were between the reasons for choice of service-learning and importance of overall civic learning goals, between the importance of civic learning goals and educational objectives on syllabus, and between planned activities and accomplished activities. This study collected the descriptive and quantitative data from the syllabi for service-learning courses and a faculty survey at Texas Tech University. The major findings were that there was meaningful consistency between: the reasons for choosing service-learning and the importance of overall civic learning goals, the importance of civic learning goals and educational objectives, and planned activities on syllabus assignment and accomplished activities on the faculty survey related to course components. Future research regarding service-learning course design would be required in detail, and practice in designing service-learning courses would be consistent between the syllabus and performance in actual courses.

• Journal of the Korea Institute of Military Science and Technology
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• v.13 no.1
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• pp.22-29
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• 2010

In this study, computational multi-body dynamics and structural vibration analyses including some impact condition have been conducted for the ground flight test system of the developed smart UAV model. Designed ground test system has four degree-of-freedom motions with limited motion control mechanism. Design safety margin designs for several structural components are tested and verified considering expected critical motions (pitching and rolling) of the test smart UAV model. Computational results for various analysis conditions are practically presented in detail. Futhermore, proper design modifications of the initially designed test equipment in order to guarantee or increase structural safety have been successfully conducted in the design stage.

• Proceedings of the Korea Water Resources Association Conference
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• 2010.05a
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• pp.1640-1644
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• 2010

In this study the wetness/dryness in Geum river basin are classified by dint of cumulative probability density function of monthly moisture index and the long term changes of them are analyzed based on climatic water balance concept. The drought events in Geum river basin are selected through evaluation of monthly moisture index and the various hydrological properties of them are investigated in detail. Also the trends of time-series of climatic water balance components are examined by Seasonal Kendall test and the variability of hydrological cycle in Geum river basin during the recent decade is inquired. It is judged that the results of this study can be contributed to establishment of the counter plan against the future drought events as the fundamental information.

• International Journal of Railway
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• v.2 no.3
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• pp.107-112
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• 2009

Research projects of SNCF aim at reducing the costs of infrastructure possessions and improving the operational equipment availability and safety. This permanent search for a better regularity led the SNCF to analyse the maintenance approach of signalling equipment in detail. Until now, it was commonly acknowledged that signalling equipment, which consists of many electronic devices, is not subject to aging. In this study, a Weibull lifetime model, able to describe an aging phenomenon, is used and it can be shown that the deterioration is statistically significant. The validity of the model is tested. We also analyse the influence of environmental covariates. We simulate different scenarios in order to investigate the impact of several maintenance strategies as well as on future maintenance costs, on the amount of components to replace based on the mean age of the network. It can be shown that in most cases a systematic replacement strategy offers the best solution.

• Journal of Environmental Science International
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• v.24 no.8
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• pp.1023-1036
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• 2015

A reliable streamflow forecasting is essential for flood disaster prevention, reservoir operation, water supply and water resources management. This study proposes a hybrid model for river stage forecasting and investigates its accuracy. The proposed model is the wavelet packet-based artificial neural network(WPANN). Wavelet packet transform(WPT) module in WPANN model is employed to decompose an input time series into approximation and detail components. The decomposed time series are then used as inputs of artificial neural network(ANN) module in WPANN model. Based on model performance indexes, WPANN models are found to produce better efficiency than ANN model. WPANN-sym10 model yields the best performance among all other models. It is found that WPT improves the accuracy of ANN model. The results obtained from this study indicate that the conjunction of WPT and ANN can improve the efficiency of ANN model and can be a potential tool for forecasting river stage more accurately.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 1999.11a
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• pp.336-339
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• 1999

Education paradigm is moved from traditional face-to-face method to cyber education environment. Therefore, we extracted the components of cyber education system and their detail functions through analysis on the workflow of education and learning standard technology. In addition, we think that template system will make a big role in order to deploy the cyber education system. Therefore, we designed the template system for cyber education. In this paper, we particularly describe both evaluation funrtion on course learning records and statistics function ell evaluation records.

• Journal of Power Electronics
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• v.2 no.4
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• pp.312-324
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• 2002

This paper presents a new PWM DC/DC converter with dual output power using single power stage, which has the isolation characteristics between each dual output. The proposed converter topology consists of two switches ($S_B$ and $S_F$) and only single secondary winding. Therefore, the proposed converter has better advantages of not only low cost and small size but also high power density because of using minimum components and devices compared with conventional methods which use multi winding transformers or several converters. The operating principle of the proposed converter topology, which includes the conventional auxiliary ZVT (Zero-Voltage-Transition) circuit to implement soft switching of the main switch, is illustrated in detail and the validity of the proposed converter is verified through several simulated and experimental results.

• Journal of Power Electronics
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• v.14 no.4
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• pp.649-660
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• 2014

A novel non-isolated bidirectional soft-switching SEPIC/ZETA converter with reduced ripple currents is proposed and characterized in this study. Two auxiliary switches and an inductor are added to the original bidirectional SEPIC/ZETA components to form a new direct power delivery path between input and output. The proposed converter can be operated in the forward SEPIC and reverse ZETA modes with reduced ripple currents and increased voltage gains attributed to the optimized selection of duty ratios. All switches in the proposed converter can be operated at zero-current-switching turn-on and/or turn-off through soft current commutation. Therefore, the switching and conduction losses of the proposed converter are considerably reduced compared with those of conventional bidirectional SEPIC/ZETA converters. The operation principles and characteristics of the proposed converter are analyzed in detail and verified by the simulation and experimental results.

• Proceedings of the KIEE Conference
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• 1996.07b
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• pp.899-901
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• 1996

KODAS is made up of the Central Control System(CCS) as four Vax workstations linked up with LAN networks, six Substation Communication Control Units(SCCU) installed in substation to transfer data, 125 Feeder Remote Units(FRU) located at the lower position of automated switch to provide the information of Fault Indicator(FI) and three kinds of automated switches to have remote control functions such as SF6 gas feeder automation switch, recloser and gas insulated pad mountes switchgear for under ground line. This paper explains the functions and characteristics in detail about each devices mentioned above.