• Journal of Digital Contents Society
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• v.9 no.4
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• pp.679-686
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• 2008

Wireless LAN(WLAN) is a rather mature communication technology connecting mobile terminals. IEEE 802.11 is a representative protocol among WLAN technologies. With the rising popularity of delay-sensitive real-time multimedia applications(video, voice and data) in IEEE 802.11 wireless LAN, it is important to study the MAC layer delay performance of WLANs. In this paper, performance for packet delay model that recently have been proposed schemes is analysed in wireless LAN and proved performance results via simulation.

• Proceedings of the KSR Conference
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• 2007.05a
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• pp.1293-1296
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• 2007

An amenity requirement of the passenger using public traffic is rising continuously, and also The Ministry of Environment established "Indoor air quality management guidelines in public facilities(Dec. 2006)". To satisfy such requirement, the photoplasma device to decrease VOCs(Volatile Organic Compounds) and suspended bacillus is applied to the underframe mounted HVAC(Heating, Ventilating and Air-Conditioning) system for train. Air purifying method of photoplasma device is optical and chemical reaction that UV-light(wavelength less than 280nm) react with catalyst material(TiO2). To analyze the efficiency of photoplasma in this study, we measured the requirement time for toluene to decease down to 0.3ppm after contaminating the passenger cabin for train to toluene 1ppm.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2000.05a
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• pp.926-929
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• 2000

Recently, there are lots of applications in machining dies using CAD/CAM systems. which results in reduction of machining time and rising of machining efficiency applying high speed machining and high quality machining. Investigation of machinability is necessary in order to apply high speed machining. In machining complicate 3D model such as connecting rod die. the need of high speed machine and coated tool is requested recently in this field. This paper introduce the database of high speed machining to improve machining efficiency of connecting rod die.

• Journal of the Korean Institute of Telematics and Electronics S
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• v.35S no.1
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• pp.60-67
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• 1998

In this paper, a gain scheduling method of PID controller is proposed using fuzzy logic for balancing control of an inverted pendulum. First, gains of PID controller are calculated using pole-placement technique for the linearized model of an inverted pendulum and these gains are modified by fuzzy logic throughout control operations. A PD controller is used by switching near the set-point to improve the performance. It is illustrated by simulations that the proposed hybrid fuzzy control method yidels smaller rising time and overshoot compared to the fixed-gain PID controller or fuzzy logic-based only PID controller.

• Proceedings of the KIEE Conference
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• 1996.07c
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• pp.1910-1912
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• 1996

This paper presents the results of laboratory experimentals to remove $SO_2$ and $NO_x$ by a pulsed corona discharge in the wire-plate reactor. A rotating spark gap switch was used to generate the pulse by chewing the dc high voltage. Repetition frequency of the pulse was 60Hz and rising time of 50ns. The photo pictures of positive streamer corona taken by ICCD camera, pulse voltage and current were measured using a digital oscilloscope. Simultaneous effects of $C_{2}H_{4}$ injection and heterogeneous chemical reactions on nonthermal plasma process to remove $SO_2$ and $NO_x$ from flue gas were investigated in the present study

• The Transactions of The Korean Institute of Electrical Engineers
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• v.58 no.1
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• pp.93-99
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• 2009

In this paper, transient voltage response of Polmer Electrolyte Membrane Fuel Cell (PEMFC) stack is analyzed and voltage dynamic characteristic is modeled for optimal design of power conditioning system (PCS). According that the load is changed, the corresponding operating voltage of fuel cell stack is also varied with a certain deep and rising time due to the chemical and mechanical responses. This transient behavior can affect on the operation with respect of PI gain in controller, duty ratio, capacitor of capacitor and so on. So in this paper the detailed theoretical analysis of transient voltage dynamics is explained and the methodology of dynamic modeling is introduced. In addition, the validity and feasibility of the proposed dynamic model is verified by experimental results under various load conditions.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2008.05a
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• pp.297-300
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• 2008

This paper presents the behaviors of transient and conventional grounding impedances of a deep-driven ground rods associated with the injection point of lightning impulse currents. The transient impedance of deep-driven ground rods under lightning impulse currents were higher than the static ground resistance. The transient grounding impedances strongly depend on the injection point and size of grounding electrodes and the rising time of impulse current. Reduction of ground system inductance is an important factor to lightning surge protection.

• 한국기계연구소 소보
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• s.18
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• pp.29-35
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• 1988

When low sliding velocities in the boundary lubrication range are operating, irregular movements frequently occur which are a result of the stick-slip phenomenon. Such slide motions are undesirable in precision machine tools, particularly with feed back systems used in numerical and adaptive control machine tools. Accordingly, this paper reports analytical and experimental studies in the stick-slip characteristic of machine tool feeding system. The main conclusions of this study are as follows; The tendency towards stick-slip effects may be reduced by; 1). Reducing the drop in friction coefficient in the Stribeck curve(on the rising part of the friction characteristic at higher sliding speeds, the system is stable all the time) 2). Reducing the transition velocity by the use of a higher viscosity lubricating oil. 3). Increasing the stiffness(Damping)and reducing normal load(Sliding mass) Therefore, the Critical velocity is decided from the above conclusions and in designing of machine tool, feed rates(sliding velocity)must be design the more than critical velocity.

• Proceedings of the KSME Conference
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• 2000.04b
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• pp.240-245
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• 2000

In this study, thickness, density and effective thermal conductivity of frost forming on the horizontal cylinder were measured with various air temperature and humidity. Reynolds number and temperature of cooling surface are controlled 17300 and $-l5^{\circ}C$ respectively. In each case of air temperature $5^{\circ}C,\;10^{\circ}C,\;15^{\circ}C,$ varying absolute humidity, experiments were executed. In measuring frost surface temperature and thickness of frost layer, infrared thermocouples and CCD camera were used. Frost was gathered from cylinder to measure mass of frost layer. Experimental data showed that the thickness and effective thermal conductivity of the frost layer increase with respect to time. Thickness of frost layer increase with humidity increasing, and density of frost layer increase with air temperature rising. Frost growth with air temperature and density of frost layer with humidity are affected by whether dew point is below or above freezing point.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.454-459
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• 2003

The one of the most important subject to develop a LPDi engine is to suppress the generation of bubble inside LPG direct injector. For the purpose of this, in this study, the analogy visualization injector to visualize the generation and behavior of bubble, is manufactured and the bubbling phenomenon and behaviors are visualized and studied. The bubble inside the injector is generated at injection hole and after rising by buoyancy, it disappear around the top of a nozzle. The number of bubble generated is little changed regardless of the lapse of time but it is increased remarkably as the temperature around the injector is increased. With injection, the temperature around the injector at which the bubble is generated in_cylinder is much lower than that without injection because the transient pressure drop of fuel by injection.