• Journal of Power Electronics
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• 제9권2호
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• pp.259-266
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• 2009

In order to increase the power density of power converters, reduction of the switching losses at high-frequency switching conditions is one of the most important issues. This paper presents a new gate drive circuit that enables the reduction of switching losses in both the Power MOSFET and the IGBT. A distinctive feature of this method is that both the turn-on loss and the turn-off loss are decreased simultaneously without using a conventional ZVS circuit, such as the quasi-resonant adjunctive circuit. Experimental results of the switching loss of both the Power MOSFET and the IGBT are shown. In addition, an energy recovery circuit suitable for use in IGBTs that can be realized by modifying the proposed gate drive circuit is also proposed. The effectiveness of both the proposed circuits was confirmed experimentally by the buck-chopper circuit.

• 대한기계학회논문집B
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• 제29권7호
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• pp.820-827
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• 2005

Development of an engine with good fuel economy is very important for successful implementation of long endurance miniature UAVs (unmanned aerial vehicles). In the study, a 4-stroke glow-plug engine was modified to a gasoline-fueled spark-ignition engine. Engine tests measuring performance and friction losses were conducted to tune a simulation program for performance prediction. It has been found that excessive friction losses are caused by insufficient lubrication at high speeds. The simulation program predicts that engine power and fuel economy get worse with high altitude due to increasing portion of friction losses. The simulation results suggest quantitative guidelines for further development of a practical engine.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2007년도 학술발표회 논문집
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• pp.126-131
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• 2007

The Imha watershed is vulnerable to severe erosion due to the topographical characteristics such as mountainous steep slopes. The RUSLE model was combined with GIS techniques to analyze the mean annual erosion losses and the soil losses caused by typhoon "Maemi". The model is used to evaluate the spatial distribution of soil loss rates under different land uses. The mean annual soil loss rate and soil losses caused by typhoon "Maemi"were predicted as $3,450\;tons/km^2/year$ and $2,920\;ton/km^2/"Maemi"$, respectively. The sediment delivery ratio was determined to be about 25% from the mean annual soil loss rate and the surveyed sediment deposits in the Imha reservoir in 1997.

• 한국화재소방학회논문지
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• 제5권2호
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• pp.21-35
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• 1991

As a part of studies of drag reduction phenomenon, at the entrance flow region of abrupt contraction tube flowing water, dilute and concentrated drag reducing polymer solutions contraction losses are estimated experimentally. Futher more, entrance lengths are considered theoretically and are measured experimentally. In the present experiment, fluid temperature is fixed l$0^{\circ}C$ and flow rates are 3,000

• 한국초전도저온공학회:학술대회논문집
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• 한국초전도저온공학회 2003년도 학술대회 논문집
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• pp.126-128
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• 2003

The effect of twisting on the microstructure and AC losses of Bi-2223 superconductor tape has been evaluated. Twisting pitches of the tapes are in the range of 12~60 mm and uniformly deformed. The critical current of the tapes was measured to decreased with decreased pitch. This reduction is believed to be due to the irregular interface, poor grain alignment. In addition, AC losses of the tape reduced as the pitch decreased probably due to combined effects of lower critical current and electrically decoupled filament of twisted tape.

• 대한전기학회논문지
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• 제34권9호
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• pp.368-375
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• 1985

This paper describes the OPTIMAL PWM strategy to reduce harmonic losses for a variaboe-speed drive of an induction motor. This OPTIMAL theory is the strategy which can reduce motor losses by defining harmonic losses as a performance index and achieving it's minimization. This PWM strategy is compared with the conventional NATURAL PWM technique by a numerical method, and verified the validity of numerical method by a result of implementing in a practical 1 Hp-3 Phase induction motor drive system. Also, we could achieve a maximum efficiency to drive an induction motor by selecting appropriately one alternative between OPTIMAL and NATURAL PWM techniques, and employing it in a full driving range.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1998년도 하계학술대회 논문집 F
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• pp.2039-2041
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• 1998

In this paper, Operation characteristics of the active clamp(ACL) zero-voltage-switching(ZVS) forward converter(FC) and active clamp hard- switching(HS) forward converter are compared with respect to loss analysis. The losses of semiconductor (including conduction losses and switching losses), transformer(containing the core loss and copper loss) and parasitic element of passive element (capacitor, inductor) are measured and compared for each type. For an experiment we have built 50W ACL ZVS-FC and ACL HS-FC, in which the switching frequency is 200kHz, and test it. The experimental results show that both types of operation have nearly same characteristics.

• KIEE International Transactions on Power Engineering
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• 제5A권2호
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• pp.193-198
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• 2005

This paper proposes a new method to handle transmission line losses using loss distribution factors (LDF) rather than marginal loss factors (MLF) in electricity market operation. Under a competitive electricity market, the bidding data are adjusted to reflect transmission line losses. To date the most proposed approach is using MLFs. The MLFs are reflected to bidding prices and market clearing price during the trading and settlement of the electricity market. In the proposed algorithm, the LDFs are reflected to bidding quantities and actual generations/ loads. Computer simulations on a 9-bus sample system will verify the effectiveness of the algorithm proposed. Moreover, the proposed approach using LDFs does not make any payments residual while the approach using MLFs induces payments residual.

• Journal of Korean Society for Atmospheric Environment
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• 제20권E2호
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• pp.61-68
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• 2004

Aerosol losses in a 100L Tedlar$^{(R)}$ bag were investigated for the aerosols with number median diameter of 0.05 ${\mu}{\textrm}{m}$ and number concentration of 6.4 ${\times}$ 10$^4$ cm$^{-3}$ . Over a 1 hr period, loss of particles in the bag is apparent, and the volume decrease with time is significant. The number concentration, surface area, and volume concentration of the aerosols decreased to 34, 50, and 52% of the initial value in 30 min, respectively. This indicates that deposition to the walls was the main loss process for aerosols in the Tedlar$^{(R)}$ bag. Theoretical calculations showed that coagulations and deposition by diffusion and gravitational sedimentation would not change aerosol characteristics significantly, and the electrical force was the dominant loss process for particles in the Tedlar$^{(R)}$ bag over a 1 hr period.eriod.

• 영어어문교육
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• 제18권3호
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• pp.93-120
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• 2012

This paper aims to address the gains and losses of the CMC environment in Language learning. Data were attained from twelve middle school ESL students who took English as a second language class and twelve pre-service teachers taking ESL foundation course. This exploration describes the role of CMC focusing on its' advantages and disadvantages which language teachers need to consider. The findings revealed that the teachers, tasks, and other elements involved in the CMC environment provided several gains and losses for many areas of learning. This implies that CMC alone does not provide an optimal learning environment, but rather it is used as an essential tool in providing opportunities to enhance language learning. Several suggestions are made for teachers and pre-service teacher education how CMC instruction might be better designed. The paper concludes with some practical considerations for future research in the area of CMC.