• Journal of KSNVE
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• v.10 no.5
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• pp.873-879
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• 2000

Experimental investigation was conducted to study the effects of pitch angle maximum camber on the performance and noise of an axial-flow fan used in outdoor-unit of air -conditioner. For this study the axial-flow fan whose pitch angle can be varied was made and the Specific sound Pressure Level and other coefficients were measured using the anechoic fan tester. It is found that pitch angle affects more severly than the maximum camber on the fan performance. On the while the maximum camber affects much on the specific sound power level. Present results show that it is important to choose the optimum pitch angle and maximum camber to design the high-performance and low-noise axial-flow fan and specific noise measured in the anechoic fan tester can be sued effectively for the design of low-noise fan.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.49 no.8
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• pp.438-444
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• 2000

We report the effects of etch process parameters on the ohmic contact formation in the plasma etching of GaN. Planar inductively coupled plasma system with $CH_4/H_2/Ar$gas chemistry has been used as etch reactor. The contact resistance and the specific contact resistance have been investigated using transfer length method as a function of RF bias power and %Ar gas concentration in total flow rate. AES(Auger electron spectroscopy) analysis revealed that the etched GaN has nonstoichiometric Ga rich surface and was contaminated by carbon and oxygen. Especially large amount of carbon was detected at the sample etched for high bias power (or voltage) condition, where severe degradation of contact resistance was occurred. We achieved the low ohmic contact of $2.4{\times}10^{-3} {\Omega}cm^2$ specific contact resistance at the input power 400 W, RF bias power 150 W, and working pressure 10mTorr with 10 sccm $CH_4$, 15 sccm H2, 5 sccm Ar gas composition.

• Membrane and Water Treatment
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• v.8 no.3
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• pp.279-292
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• 2017

This study was aimed at ultrafiltration (UF) as a pretreatment before reverse osmosis (RO) within the scheme of hybrid reverse osmosis-multistage flush (RO-MSF) desalination. Seawater at elevated temperature (after MSF heat-exchangers) was used as a feed in this process. The pretreatment system was represented as a set of functionally-linked technological segments such as: UF filtration, backwashing, chemical- enhanced backwashing, cleaning, waste disposal, etc. The process represents the sequences of operating cycles. The cycle, in turn, consists of the following unit operations: filtration, backwashing and chemical-enhanced backwashing (CEB). Quantitative assessment was based on the following indicators: normalized permeability, transmembrane pressure, specific energy and water consumption, specific waste generation. UF pre-treatment is accompanied by the following waste streams: $W1=1.19{\times}10$ power of $-2m^3$ (disposed NaOCl with 0.0044% wt.)/$m^3$ (filtrate); $W2=5.95{\times}10$ power of $-3m^3$ (disposed $H_2SO_4$ with 0.052% wt.)/$m^3$(filtrate); $W3=7.26{\times}10$ power of $-2m^3$ (disposed sea water)/$m^3$ (filtrate). Specific energy consumption is $1.11{\times}10$ power of $-1kWh/m^3$ (filtrate). The indicators evaluated over the cycles with conventional (non-chemical) backwashing were compared with the cycles accompanied by CEB. A positive impact of CEB on performance indicators was demonstrated namely: normalized UF resistance remains unchanged within the regime accompanied by CEB, whereas the lack of CEB results in 30% of its growth. Those quantitative indicators can be incorporated into the target function for solving different optimization problems. They can be used in the software for optimisation of operating regimes or in the synthesis of optimal flow- diagram. The cycle characteristics, process parameters and water quality data are attached.

• Journal of the Institute of Electronics and Information Engineers
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• v.50 no.7
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• pp.109-114
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• 2013

Power MOSFET (metal-oxide semiconductor field-effect transistor) are widely used in power electronics applications, such as BLDC (Brushless Direct Current) motor and power module, etc. For the conventional power MOSFET device structure, there exists a tradeoff relationship between specific on-state resistance and breakdown voltage. In order to overcome the tradeoff relationship, a non-uniform super-junction (SJ) trench MOSFET (TMOSFET) structure for an optimal design is proposed in this paper. It is required that the specific on-resistance of non-uniform SJ TMOSFET is less than that of uniform SJ TMOSFET under the same breakdown voltage. The idea with a linearly graded doping profile is proposed to achieve a much better electric field distribution in the drift region. The structure modelling of a unit cell, the characteristic analyses for doping density, and potential distribution are simulated by using of the SILVACO TCAD 2D device simulator, Atlas. As a result, the non-uniform SJ TMOSFET shows the better performance than the uniform SJ TMOSFET in the specific on-resistance at the class of 100V.

• The Korean Journal of Financial Management
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• v.21 no.1
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• pp.183-204
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• 2004

This paper introduces an observable connection structure between stocks in Korean stock market and investigates the formation principles of the observed connection structure between stocks in economic views. Several recent studies have been attempting to explain that the connection structure between stocks is organized by Power-Law distribution, this implies that most stocks have a few links, but only a few stocks have very large number of links. Therefore, we want to investigate the reason about why the connection structure between stocks exhibited by Mantegna's approach is Power-Law distribution. As a result we found that the number of connection between stocks is determined by market factors and specific firm factors among many other factors. In addition, if a stock is more affected by common factors(market) than specific firm factors, the stock has large number of links with other stocks, otherwise more affected by specific firm factors, the stock has a few links.

• Journal of Korean Tunnelling and Underground Space Association
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• v.20 no.4
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• pp.687-699
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• 2018

The construction of subsea tunnel differs from that of inland tunnel because of high water pressure due to sea water level and difficulties to reinforce the ground under construction. Therefore, it is very important to prevent trouble in advance when the subsea tunnel is constructed. In this paper, we established lots of databases about characteristics of geological and mechanical parameters on the construction of subsea tunnel using micro slurry TBM which depth is about 60 m. The correlation analysis is conducted to confirm the effect of thrust, torque and RPM among the excavation database on the net penetration rate. Also, An empirical formula is suggested to predict the net penetration rate through the correlation analysis between FPI (Field Penetration Index) and specific energy from the subsea tunnel excavation database.

• IEMEK Journal of Embedded Systems and Applications
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• v.2 no.3
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• pp.194-201
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• 2007

As the performance of the mobile terminal becomes higher, the power consumption gradually increases. As a result, power management is one of the most important issues in mobile system with battery. In this paper, we describe an DPM(Dynamic Power Management) using DVS(Dynamic Power Management) as a power management mechanism in Qplus operating system. DVS generally considers a specific device such as CPU, whereas we consider the relations with other hardware components as well as each component. We specially focus on the relation between CPU, memory and LCD devices. We also designs a kernel monitor to collect information to decide the policy for power management. According to the experimental results, the proposed method enables to save much power.

• Journal of the Korean Institute of Navigation
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• v.24 no.3
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• pp.147-155
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• 2000

In this paper, we propose the Chaos Fuzzy controller to analyze the chaotic character of time series obtained from the specific plant and to predict the short-term for power consumption of the plant using the Fuzzy controller. We compared the predicted data with the active ones and checked the error generated by them after we time series of supplied power to the proposed controller. As a result of the simulation, we obtained a admirable consequence that the proposed controller can be advanced through various and accurate data acquisition, and continuous analysis of the resident and industrial environment.

• Proceedings of the KIPE Conference
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• 1998.10a
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• pp.535-540
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• 1998

This paper discusses a triple stage current source GTO inverter system for high power motor drives. The energy rebound circuit of the triple stage inverter not only controls the spike voltage of the GTO inverter but also facilitates PWM control of the thyristor rectifier operated at unity fundamental input power factor. Based on Pspice simulation and experiments, the principles and PWM pulse pattern for removing specific lower harmonics in the inverter's output current are discussed in detail.

• Proceedings of the KIPE Conference
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• 2010.07a
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• pp.178-179
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• 2010

This paper presents a simulation model and analysis of grid-tied wind turbine generator with batteries using the PSCAD/EMTDC software. The modeled system is consist of two inverters and one bidirectional DC/DC converter. These inverter are to capture the maximum active power under varying wind conditions and to keep the DC-Link voltage magnitude at a specific level. And the bidirectional DC/DC converter makes battery charging or discharging depend on power gap between wind turbine output and local load. Aerodynamic models are applied for a wind turbine blade simulator.