• Journal of Information Technology Applications and Management
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• v.18 no.1
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• pp.75-100
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• 2011

For decades, thousands of corporation introduced knowledge management systems to respond knowledge-based society. However, it seems that the systems merely focusing on knowledge accumulation and its sharing have been bounded by many restrictions in terms of new knowledge creation based on the life cycle of knowledge management systems. Moreover, recently, a variety of knowledge management activities regarding organization, systems, and process is emphasized as a strategic asset for a corporation to create core knowledge. Therefore, this study adopted the Csikszentmihalyi's flow theory to investigate the factors affecting knowledge creation and the success factors of knowledge management systems in virtual space. Prior studies argued that flow experience should be a prerequisite for creative knowledge creation. In that vein, this research revealed the causal relationships for flow experience between the determinants of clear goal, immediate feedback, congruence of challenge and skill. Additionally, it empirically examined how flow experience affected the exploratory behavior of knowledge creation.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.1
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• pp.61-66
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• 2010

In our previous work, 3-dimensional hydrodynamic focusing microfluidic device (3D-HFMD) has been developed with the help of locally increased aspect ratio of thickness to width without any horizontal separation wall. In this study, we have investigated 3-dimensional hydrodynamic focusing behaviors inside the 3D-HFMD according to the various geometric and flow conditions. The parametric study has been extensively carried out for the effects of geometric and flow conditions on 3-dimensional hydrodynamic focusing with both 3D-HFMD and previous microfluidic device design based on three-dimensional computational fluid dynamics (CFD) simulations. The CFD simulations suggested the proper design window of channel geometry and flow conditions.

• Journal of Biomedical Engineering Research
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• v.36 no.3
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• pp.61-68
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• 2015

In this paper, we studied the effects of intersection angles of the flow-foucusing type droplet generation device inlet channel on droplet diameter using numerical simulation modeling. We modeled different intersection angles with a fixed continuous channel width, dispersed channels width, orifices width, and expansion channels width. Numerical simulations were performed using COMSOL Multiphysics$^{(R)}$ to solve the incompressible Navier-Stokes equations for a two-phase flow in various flow-focusing geometries. Modeling results showed that an increase of the intersection angle causes an increase in the modification of the dispersed flow rate ($v^{\prime}{_d}$), and the increase of the modification of the continuous flow rate ($v^{\prime}{_c}$) obstructs the dispersed phase fluid flow, thereby reducing the droplet diameter. However, the droplet diameter did not decrease, even when the intersection angle increased. The droplet diameter decreased when the intersection angle was less than $90^{\circ}$, increased at an intersection angle of $90^{\circ}$, and decreased when the intersection angle was more than $90^{\circ}$. Furthermore, when the intermediate energy deceased, there was a decrease in the droplet diameter when the intersection angle increased. Therefore, variations in the droplet diameter can be used to change the intersection angle and fluid flow rate.

• Journal of Industrial Technology
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• v.35
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• pp.73-80
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• 2015

This paper is research results of the case study on analyzing the characteristics of debris flow considering forest environmental factors, focusing on occurrence of landslides around Mt. Daeryoung in 2013. Extensive landslide of debris flow, caused by heavy rainfall, occurred around Mt. Daeryoung during July in 2013. Field investigation was carried out to construct the data base about forest environmental factor including topography, soil formations and forest type. Thus, contributing factors to cause the landslide of debris flow were investigated so that damages from landslides could be reduced by establishing proper measures.

• Proceedings of the KIEE Conference
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• 2002.07c
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• pp.1991-1993
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• 2002

This paper presents the PDMS surface characteristic change after the plasma process and the electroosmotic flow control technique for the two-dimensional focusing in the micro channels made of PDMS and glass. The channels are fabricated by plastic molding and micromachining technique. To observe the surface characteristic change as time elapses, we measure the contact angle of water on the surface and the velocity of the electroosmotic flow in a channel. The electric field adequate for focusing of a core flow in a confluence channel is obtained by the experiment. The computer simulation is performed to obtain the width and the depth of the core flow for several junction angles of the confluence channel.

• Proceedings of the KSME Conference
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• 2008.11b
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• pp.2692-2695
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• 2008

Polydiacetylene (PDA) is chemosensor materials that exhibit non-fluorescent-to-fluorescent transition as well as blue-to-red visible color change upon chemical or thermal stress. They have been studied in forms of film or microarray chip, so far. In this paper, we provide a novel technique to fabricate continuous micro-fiber PDA sensor using in-situ laser-polymerization technique and 3-D hydrodynamic focusing on a microfluidic chip. The flow of a monomer solution with diacetylene (DA) monomer is focused by a sheath flow on a 3-D microfluidic chip. The focused flow is exposed to 365 nm UV laser beam for in-situ polymerization which generates a continuous fiber containing DA monomers. Then, the fiber is exposed to 254 nm UV light to polymerize DA monomers to PDA. Preliminary results indicate that the fiber size can be controlled by the flow rates of the monomer solution and sheath flows and that a PDA sensor fiber successively responds to chemical and thermal stress.

• Nuclear Engineering and Technology
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• v.30 no.2
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• pp.148-163
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• 1998

Flow Induced Material Degradation (FIMD) is reviewed focusing on Flow Accelerated Corrosion (FAC) models. Several examples of FAC related incidents are described, which include nuclear and fossile power plants. Lastly, mitigation techniques such as inspection, material selection, water chemistry, temperature, and hydrodynamic factor are discussed.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.1505-1509
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• 2004

A novel technique for fine particle beam focusing under the atmospheric pressure is introduced using a radiation pressure assisted aerodynamic lens. To introduce the radiation pressure in the aerodynamic focusing system, a 25 mm plano-convex lens having 2.5 mm hole at its center is used as an orifice. The particle beam width is measured for various laser power, particle size, and flow velocity. In addition, the effect of the laser characteristics on the beam focusing is evaluated comparing an Ar-Ion continuous wave laser and a pulsed Nd-YAG laser. For the pure aerodynamic focusing system, the particle beam width was decreased as increasing particle size and Reynolds number. For the particle diameter of 0.5 ${\mu}m$, the particle beam was broken due to the secondary flow at Reynolds number of 694. Using the Ar-Ion CW laser, the particle beam width becomes smaller than that of the pure aerodynamic focusing system about 16 %, 11.4 % and 9.6 % for PSL particle size of 2.5 ${\mu}m$, 1.0 ${\mu}m$, and 0.5 ${\mu}m$ respectively at the Reynolds number of 320. Particle beam width was minimized around the laser power of 0.2 W. However, as increasing the laser power higher than 0.4 W, the particle beam width was increased a little and it approached almost a constant value which is still smaller than that of the pure aerodynamic focusing system. The radiation pressure effect on the particle beam width is intensified as Reynolds number decreases or particle size increases relatively. On the other hand, using 30 Hz pulsed Nd-YAG laser, the effect of the radiation pressure on the particle beam width was not distinct unlike Ar-Ion CW laser.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.8 s.227
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• pp.1190-1195
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• 2004

A novel manipulation of microfluid width in a microchannel was presented by controlling inflation of a gas boundary. The gas boundary was formed by heating water with a microheater in a semicircular shape from a chamber which was connected symmetrically to the microchannel. The formed gas boundary inflated perpendicularly to the flow direction and, consequently, the microfluid width was narrowed. The inflation and contraction were flexibly like a virtual wall and dependent on two factors: one is the flow velocity of the microfluid and the other is the pressure inside the gas boundary. Dimensions of the chamber and the microchannel width were determined empirically as same of $300\;{\mu}m$ for stable operation. The width of microfluid was manipulated manually with the microheater and could be maintained as up to $22\;{\mu}m$. The stable focusing began to be distorted when the flow velocity exceeded 17.8 mm/s.

• 한국연소학회:학술대회논문집
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• 2012.11a
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• pp.323-324
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• 2012

Flammability limits of opposed flow diffusion flame in a narrow channel was investigated experimentally and theoretically. There were three different extinction modes corresponding to high strain rate (HSR), low strain rate (LSR) and dilution ratio (DR) limits. To investigate these limits, a theoretical study was followed by focusing on flow and heat transfer characteristics. Consequently, a dead space concept that has been used for premixed flames was important to reveal the heat loss mechanism in a narrow channel especially for LSR conditions even in the case of diffusion flames.