• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.1
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• pp.63-69
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• 2004

It is of great interest to enhance mixing performance in a microchannel in which the flow is usually characterized as a low Reynolds number (Re) so that good mixing is quite difficult to be achieved in this laminar flow regime. In this regard, we present a new chaotic passive micromixer, named Barrier Embedded Micromixer (BEM), of which the mixing mechanism is based on chaotic flows. In BEM, chaotic flow is induced by periodic perturbation of the velocity field due to periodically inserted barriers along the channel wall while a helical type of flow is obtained by slanted grooves on the bottom surface of the channel in the pressure driven flow. To experimentally compare the mixing performance, a T-microchannel and a microchannel with only slanted grooves were also fabricated. All microchannels were made of PDMS (Polydimethylsiloxane) from SU-8 masters that were fabricated by conventional photolithography. Mixing performance was experimentally characterized with respect to an average mixing intensity by means of color change of phenolphthalein as pH indicator. It was found that mixing efficiency decreases as Re increases for all three micromixers. Experimental results obviously indicate that BEM has better mixing performance than the other two. Chaotic mixing mechanism, suggested in this study, can be easily applied to integrated microfluidic systems , such as Micro-Total-Analysis-System, Lab-on-a-chip and so on.

• Journal of the Korean Society for Precision Engineering
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• v.23 no.4 s.181
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• pp.116-123
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• 2006

During the last two decades, many researchers investigated influences of stress triaxiality on ductile fracture for various specimens and structures. With respect to a transferability issue, the local approach reflecting micro-mechanical specifics is one of effective methods to predict constraint effects. In this paper, the applicability of the local approach was examined through a series of finite element analyses incorporating modified GTN (Gurson-Tvergaard-Needleman) and Rousselier models as well as fracture toughness tests. To achieve this goal, fracture resistance (J-R) curves of several types of compact tension (CT) specimens with various crack length, with various thickness and with/without 20% side- grooves were estimated. Then. the constraint effects were examined by comparing the numerically estimated J-R curves with experimentally determined ones. The assessment results showed that the damage models might be used as useful tool for fracture toughness estimation and both the crack length and thickness effects should be considered for realistic structural integrity evaluation.

• Journal of the Korean Ceramic Society
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• v.40 no.1
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• pp.104-108
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• 2003

COF(Coefficient Of Friction), AE(Acoustic Emission), micro-cracks and crystal structure of the single crystalline silicon were investigated according to the induced normal load during scratching test. Scratching tests were performed with the loading rate of 100 N/min and various scratching speeds of 1, 3, 6, 10 mm/min from 0 up to 30 N of the maximum normal load. In consequence, COF, AE and crack density were observed to increase with increasing normal load or increasing scratching speed. Phase transformations from the silicon diamond structure to other structures were observed in the scratched grooves for the slow scratching speeds using micro-Raman spectroscopy.

• Transactions of Materials Processing
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• v.13 no.4
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• pp.326-333
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• 2004

The nanoprobe based on lithography, mainly represented by SPM based technologies, has been recognized as a potential application to fabricate the surface nanosctructures because of its operational versatility and simplicity. However, nanoprobe based on lithography itself is not suitable for mass production because it is time a consuming method and not economical for commercial applications. One solution is to fabricate a mold that will be used for mass production processes such as nanoimprint, PDMS casting, and others. The objective of this study is to fabricate the silicon stamper for PDMS casting process by a mastless fabrication technique using the combination of nano/micro machining by Nanoindenter XP and KOH wet etching. Effect of the Berkovich tip alignment on the deformation was investigated. Grooves were machined on a silicon surface, which has native oxide on it, by constant load scratch (CLS), and they were etched in KOH solutions to investigate chemical characteristics of the machined silicon surface. After the etching process, the convex structures was made because of the etch mask effect of the mechanically affected layer generated by nanoscratch. On the basis of this fact, some line patterns with convex structures were fabricated. Achieved groove and convex structures were used as a stamper for PDMS casting process.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.16 no.12
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• pp.1110-1114
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• 2003

We have investigated the generation of pretilt angle for a nematic liquid crystal (NLC) alignment with rubbing alignment method on polyimide surfaces using thin plastic substrates. It was found that monodomain alignment of NLC is obtained with rubbing alignment method on polyimide surfaces using thin plastic substrates. The NLC pretilt angles generated are about 3$^{\circ}$ by the rubbing alignment method on thin plastic substrates, However, the pretilt angle are at about 1.7$^{\circ}$ lower on the glass substrate than on thin plastic substrate. We obtain that AFM (atomic force microscope) image of rubbed PI surface with polymer film has formed the micro-groove structure at the low curring temperature (120$^{\circ}C$). However, no grooves are obtained on the glass substrate at the same temperature. It is considered that this alignment may be attributed to roughness of micro-groove substrate. The tilt angle increases with increasing baking temperature for making polyimide layer using glass substrate. It was concluded that the pretilt angle in the polyimide surface is attributable to the increasing of imidization rato.

• Textile Coloration and Finishing
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• v.13 no.6
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• pp.428-434
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• 2001

This study surveys the fiber behavior in yam formation and the Physical properties of Solo-spun yarn. The specimens were made by six types of Solo-spun rollers with fixed twist multiplier In the previous part, the physical properties such as yarn count, evenness, strength, and breaking elongation of these yams were compared with the properties of ring shun yarns and analysed with the mechanism of Solo-spun yarn formation. In the second part of this report, the abrasion resistance and hairiness were discussed wish respect to the micro yarn structures. The narrower the groove width of Solo-spun roller is, the more active the bulk fibers migration is. The Solo-spun film structure has two groups. One is shorter than the others one in longitudinal direction of yarn and has the same structure as ring-spun yarn, which is derided from the smooth zone on the surface of Solo-spun roller. The other one is longer than the former and there are the wrapping fibers. This part is derived from the conflicted grooves on the surface of Solo-spun troller.

• Textile Coloration and Finishing
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• v.13 no.6
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• pp.70-70
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• 2001

This study surveys the fiber behavior in yarn formation and the Physical properties of Solo-spun yarn. The specimens were made by six types of Solo-spun rollers with fixed twist multiplier In the previous part, the physical properties such as yarn count, evenness, strength, and breaking elongation of these yarns were compared with the properties of ring spun yarns and analysed with the mechanism of Solo-spun yarn formation. In the second part of this report, the abrasion resistance and hairiness were discussed with respect to the micro yarn structures. The narrower the groove width of Solo-spun roller is, the more active the bulk fiber migration is. The Solo-spun yarn structure has two groups. One is shorter than the other one in longitudinal direction of yarn and has the same structure as ring-spun yarn, which is derived from the smooth zone on the surface of Solo-spun roller. The other one is longer than the former and there are the wrapping fibers. This part is derived from the conflicted grooves on the surface of Solo-spun roller.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.10a
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• pp.351-354
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• 2004

This work presents a simple and cost-effective approach for maskless fabrication of positive-tone silicon master for the replica molding of hyperfine elastomeric channel. Positive-tone silicon masters were fabricated by a maskless fabrication technique using the combination of nanoscratch by Nanoindenter ⓡ XP and XOH wet etching. Grooves were machined on a silicon surface coated with native oxide by ductile-regime nanoscratch, and they were etched in a 20 wt％ KOH solution. After the KOH etching process, positive-tone structures resulted because of the etch-mask effect of the amorphous oxide layer generated by nanoscratch. The size and shape of the positive-tone structures were controlled by varying the etching time (5, 15, 18, 20, 25, 30 min) and the normal loads (1, 5 mN) during nanoscratch. Moreover, the effects of the Berkovich tip alignment (0, 45$^{\circ}$) on the deformation behavior and etching characteristic of silicon material were investigated.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.1136-1141
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• 2003

Among various methods to manufacture the PDP barrier ribs, the pressing and the roll forming methods are simple and economical because they form the ribs by utilizing the plastic flow of the green tape in a relatively short time without generating air-polluting dusts. In the present study, the roll forming method was investigated by experiments as well as numerical analyses and in result the groove roll and the preform were designed. The effect of draft angle, comer radius, and initial thickness of the green tape on the plastic flow was examined by a series of parametric studies. The preform was recommended to ease the plastic flow into the grooves and to avoid the occurrence of crack during rolling and sintering processes.

• Laser Solutions
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• v.15 no.2
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• pp.6-10
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• 2012

We fabricated the diffraction grating on the surface of fused silica glass using a femtosecond laser. The grooves of diffraction grating has a lot of micro crack and debris result in reduced diffraction efficiency. So, we polished the diffraction grating with $CO_2$ laser beam. With different scan number of $CO_2$ laser beam, we observed the image of diffraction grating and measured the diffraction efficiency.