• Proceedings of the Membrane Society of Korea Conference
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• 1997.04a
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• pp.87-109
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• 1997

Reverse osmosis(R/O), ultrafiltration(UF) and microfiltration (MF) processes are widely used for water treatment. In the seminar, characteristics of typical membrane modules including tubular, hollow fiber, plate and frame and spiral wound types will be discussed in detail. The design methods based on hydrodynamics for hollow fiber and spiral wound modules will be introduced analytically. Concentration polarization (CP) and membrane fouling mechnism as well as the techniques for CP reduction will be handled. The CP control techniques contain chemically modified membrane surface, pretreatment of feed water, operation of low trans-membrane pressure, chemical or physical cleaning methods and artificial production of various fluid turbulences near the membrane surface, etc. In especially, the recent commercial membrane modules for CP control including module rotation, vibration and Taylor or Dean vortex system will be introduced and discussed in detail.

• Journal of the Korean Ceramic Society
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• v.35 no.6
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• pp.575-582
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• 1998

Sutiability of Jungsan clay shale dolomite sludge Anyang feldspar and alumina as raw materials for light-weight porous ceramics was examined. In order to find optimum manufacturing conditions compositions heating temperatuers and heating times were varied and their effects on physical properties were measured and bloating mechanism was investigated. Jungsan clay seems suitable as raw material to make the light-weight constructional materials with 5wt% of ANyang feldspar and alumina added in calcined clay (800$^{\circ}C$) having bulk density of 0.45g/cm3 water absorption of 1.34% and compressive strength of 85kg/cm2 rapid-heated at 1200$^{\circ}C$ for 30min. It is suggested that bloating mechanism depends on the difference of tem-peratures between the inside and outside in specimen the remained gases in interstices can bloat by the li-quid phase of surface with high viscosity and gas pressure at elevated temperature.

• Journal of the Korean Institute of Telematics and Electronics
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• v.26 no.4
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• pp.45-52
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• 1989

The size of links and actuators of robots tends to be overdesigned compared with their performance. It is recently reported that the balancing of a robot links simplifies its dynamics and eliminates the gravity terms. As a way of avoiding overdesign problem, an auto-balancing mechanism is proposed, which enables to satisfy varying balancing condition according to payloads. The performance of this auto-balancing mechanism is illustrated by the computer simulation evidences.

• Proceedings of the IEEK Conference
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• 2007.07a
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• pp.3-4
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• 2007

Wireless Sensor Network is a form of network which consumes relatively less data trasmisson rate and energy. In this type of network, minimizing the consumption of energy so that it maximizes life time is very important. To be able to improve the energy comsumption, we propose the mechnism to trasmit broadcasted packet according to level value with priority assiagned to each relay node.

• Restorative Dentistry and Endodontics
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• v.21 no.1
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• pp.161-173
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• 1996

The cariostatic effect of fluoride had been established by many epidemiologic and experimental studies. But, there are still different views on the mechnism of cariostasis and remineralization, especially about the proper fluoride concentration. The purpose of this study is to ascertain the remineralization of caries lesion and influence of fluoride concentration which affect remineralization by a study based on dynamic mechanism. The subjects, sound permanent teeth without demineralization or crack, were immersed in lactic acid buffered demineralization solution for 4 days. Dental caries with surface zone and subsurface lesion were artificially produced. All specimens were immersed in lactic acid buffered remineralization solution which had fluoride concentrations of 1 ppm, 2 ppm, 3 ppm for 10days. Final conclusions were obtained by observing the specimens for every 10 days under polarized microscopy. 1. Remineralization of caries lesion as well as demineralization of enamel were produced by changing the degree of saturation of lactic acid buffer solution. 2. Remineralization of caries lesion was facillitated by fluoride ion in lactic acid buffer solution. but, remineralization of the entire caries lesion was not increased as fluoride ion concentration increased.

• Journal of the Korean Society of Safety
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• v.19 no.2
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• pp.26-33
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• 2004

This study presents a hazard assessment of the human body exposed to electic shock considering various parameters which affect severity of the electric shock. The present study has two research objectives; one is no analyze hazards of the human body by the elctric shock both on the ground and in the water. The other is to understand the mechnism of the electric shock. In order to achieve these objectives the hazard of shock is estimated by comparing with physiological effects of electric curren througn the human body according to variation of shock parameters of shock circuits. The shock parameters adopted in this paper consist of body resistance, resistance of protective equipment, ground resistance, shock duration, depth of gound surface layer, relection factor, permissible touch voltage, body current and body voltage. Besides, safety standard determining hazard degree of the human body is introduced. And hazard of the human body due to the electric shock is quantitatibely assessed in consideration of data obtained by the method suggested herein, and final results are presented and discussed.

• 한국연소학회:학술대회논문집
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• 2002.06a
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• pp.52-60
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• 2002

A two-dimensional direct numerical simulation is performed to investigate the flame structure of $CH_4/N_2-Air$ counterflow nonpremixed flame interacting with a single vortex. The detailed transport properties and a modified 16-step augmented reduced mechanism based on Miller and Bowman's detailed reaction mechanism are adopted in this calculation. To quantify the strain on flame induced by a vortex, a scalar dissipation rate (SDR) is introduced. Results show that the fuel and air-side vortex cause an unsteady extinction. In this case, the flame interacting with a vortex is extinguished at much larger SDR than steady flame. It is also found that air-side vortex extinguishes a flame more rapidly than fuel-side vortex. The unsteady effect induced by flame-vortex interaction does not lead to a transient OH overshoot of the maximum steady concentration observed in experiment, while $HO_2$ radical increases more than the maximum steady concentration with increasing SDR. In addition, it is seen that NO and $NO_2$ are not sensitive to the unsteady variation of SDR.

• Journal of Advanced Marine Engineering and Technology
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• v.9 no.4
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• pp.328-338
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• 1985

When the low temperature service steels are used as materials for welded structure, some problems-brittleness and weld cracking, etc.-occur in welded part due to the change of mechanical and metallurgical characteristics resulted from the thermal cycle during the welding procedure. In this study, the experiments were conducted to investigate the change of mechanical and metallurgical characteristics of the welded part for the low temperature and high pressure service steels. Moreover, the Static and Dynamic Implant Test Method was introduced to this study in order to find out the mechnism of weld cracking. In addition, the fracture toughnesses of welded bond were inspected under the various low temperature environments. Main results obtained are as follows; 1) The effect of the hydrogen on the fatigue characteristics of the weld bond can be estimated by the new self-contrived Dynamic Implant Test equipment. 2) The fine micro-structure and low hardness in the heat affected zone can be obtained by the small heat input multi-pass welding. 3) The susceptibility of the delayed cracking is largely affected by the condition of used electrode. 4) The transition temperature of the fracture surface in weld bond appears to be higher 20 .deg. C than that in base metal.

• Journal of Sensor Science and Technology
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• v.12 no.3
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• pp.112-120
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• 2003

The composite of ionic polymer and metal has been fabricated and used for actuators. Platinum is deposited by electroless plating method onto the both sides of ionic polymer where ac voltage is applied. This results in the bending motion of a beam type actuator. In this paper, the fabrication method of ionic polymer-metal composite has been explained and the moving mechanism has been fabricated and measured using the ionic polymer-metal composite actuator. The moving mechanism is wireless type and the power is supplied through the rail electrodes in base plate. The maximum speed of the moving mechanism was about 24cm/min.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.11 no.8
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• pp.646-651
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• 1998

In this present study, the luminescence characteristics and mechanism of energy $CaTiO_3$:Pr phosphor were studied using disk specimens sintered at various temperatures and envirenment. A single-phase $CaTiO_3$:Pr was synthesized by sintering above 140$0^{\circ}C$ and its crystal structure was found to be perovskite orthorhombic. A dominant peak around 360 nm and a broad peak around 395 nm were observed in the PLE(Photoluminescence Excitation) spectrum of $CaTiO_3$:Pr with fixed emission wavelength at 612 nm, the decay time of 360 nm excitation was found to be longer than that of 395 nm excitation. From this result, it is assumed that the free carrier excited to 360 nm is transferred to 395 nm energy level. Therefore, the decrease in 395 nm intensity observed in CaTiO$_3$:Pr specimens sintered in Ar gas environment induced shorter decay time and improved CL luminescence.