• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.1
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• pp.109-117
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• 2004

The objective of this study is to investigate the effect of the spray characteristics on the etching characteristics for the optimization of etching process in the micro fabrication industry. The etching characteristics such as etching rate and etching factor were investigated under different etching conditions. To compare with the etching characteristic, the spray characteristics such as droplet size and velocity were measured by PDA system. The etching rate was increased in case of high spray pressure and in the region of spray center. The etching factor was increased with decrease in the distance from nozzle tip and increase in the etchant temperature. It was found that the spray characteristics were correlated with the etching characteristics.

• Transactions of the Korean Society of Mechanical Engineers
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• v.5 no.4
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• pp.338-346
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• 1981

Honing, lapping, polishing and superfinishing are applied for a precision machining to finish the metal surface, but these precision machining are micro-cutting by hard and micro-abrasive grains. Frictional machining is the new method to finish mirrorlike surface without using those abrasive grains. The frictional machining produces high pressure and high temperature instantly by compressing a tool material against the metal surface in sliding motion. The metal surface is given plastic deformation and plastic flow by the above mentioned frictional motion, but the surface roughness of the metal surface is influenced by physical and chemical reaction in surrounding atmosphere. Therefore, the atmosphere around the metal optimum atmosphere in the frictional machining. The part 1 of the study was performed in liquid atmospheres. Diesel oil, lubricant, grease, lard oil, bean oil and cutting fluid were used as such atmospheres. Medium carbon steel SM 50 C was used as a workpiece and ceramic tip was applied as a frictional tool. The result of the experiment showed characteristic machining conditions to generate the best surface roughness in each atmospheres.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.10a
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• pp.245-249
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• 2002

Tungsten carbide microshaft is used as various micro-tools in MEMS because it has high hardness and good rigidity. In this study, experiments were performed to produce tungsten carbide microshaft using electrochemical machining. $H_2SO_4$solution was used as electrolyte because it can dissolve tungsten and cobalt simultaneously. Optimal electrolyte concentration and machining voltage satisfying uniform shape and large MRR of workpiece were found. For one-step machining, the immersion depth over 1 mm was selected for avoidance of concentration of electric charge at the tip of the microshaft. The limit diameter with good straightness was shown and an empirical formula for WC-microshaft machining was suggested. By controlling the various machining parameters, a straight microshaft with 30 $\mu\textrm{m}$ diameter, over 1 mm length and under 0.5$^{\circ}$ taper angle was obtained.

• Journal of Institute of Convergence Technology
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• v.1 no.1
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• pp.48-51
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• 2011

Transdermal drug delivery device is a method of drug delivery through the skin. Skin has a very large area, so it is attractive route to drug delivery. When drug delivery through the skin, microneedle has a advantage that painless, constant drug deliver and penetration efficient; nevertheless the cost is expensive because fabrication process need a particular equipment and not suitable in mass production. This study shows microneedle fabrication process using convergence of general MEMS process and dicing process that can make 3-D sharp microneedle tip and this fabrication process suitable for mass production.

• Restorative Dentistry and Endodontics
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• v.46 no.4
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• pp.56.1-56.11
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• 2021

Objectives: This study evaluated 2 nickel-titanium rotary systems and a complementary protocol with an ultrasonic tip and a small-diameter instrument in flattened root canals. Materials and Methods: Thirty-two human maxillary second premolars with flattened canals (buccolingual diameter ≥4 times larger than the mesiodistal diameter) at 9 mm from the radiographic apex were selected. The root canals were prepared by ProDesign Logic (PDL) 30/0.01 and 30/0.05 or Hyflex EDM (HEDM) 10/0.05 and 25/0.08 (n = 16), followed by application of the Flatsonic ultrasonic tip in the cervical and middle thirds and a PDL 25/0.03 file in the apical third (FPDL). The teeth were scanned using micro-computed tomography before and after the procedures. The percentage of volume increase, debris, and uninstrumented surface area were analyzed using the Kruskal-Wallis, Dunn, Wilcoxon, analysis of variance/Tukey, and paired and unpaired t-tests (α = 0.05). Results: No significant difference was found in the volume increase and uninstrumented surface area between PDL and HEDM (p > 0.05). PDL had a higher percentage of debris than HEDM in the middle and apical thirds (p < 0.05). The FPDL protocol resulted in less debris and uninstrumented surface area for PDL and HEDM (p < 0.05). This protocol, with HEDM, reduced debris in the middle and apical thirds and uninstrumented surface area in the apical third (p < 0.05). Conclusions: High percentages of debris and uninstrumented surface area were observed after preparation of flattened root canals. The HEDM, Flatsonic tip, and 25/0.03 instrument protocol enhanced cleaning in flattened root canals.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.8
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• pp.875-880
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• 2014

Recently, three-dimensional scaffolds and nanofibers are being developed for bone tissue regeneration. In this study, we fabricated a hybrid scaffold using a nano-micro precision deposition system. The fabrication process involved the application of the solid freeform fabrication (SFF) technology and electrospinning. The hybrid scaffolds were combined using micro scaffolds and nanofibers. The nanofibers were deposited on each layer of the micro scaffolding using the electrospinning process. The micro scaffolds were fabricated using the SFF technology at a temperature of $100^{\circ}C$, pressure of 650 kPa, and scan velocity of 250 mm/s. Nanofiber fabrication was conducted by means of electrospinning using the flow rate, solution concentration, distance from the tip to the collector (TCD), and voltage. The nanofibers were fabricated using a flow rate of 0.1 ml/min, voltage of 5 kV, TCD of 1 mm, and 10 wt% of solution concentration. MG-63 cells were seeded into the hybrid scaffold for the purpose of its evaluation.

• Tribology and Lubricants
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• v.21 no.3
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• pp.107-113
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• 2005

Micro/nano adhesion and friction properties of self-assembled monolayers (SAMs) with different head- and end-group were experimentally studied according to the coating methods. Various kinds of SAM having different spacer chains (C10 and C18), head-group and end-group were deposited onto Si-wafer by dipping and chemical vapour deposition (CVD) methods under atmospheric pressure, where the deposited SAM resulted in the hydrophobic nature. The adhesion and friction properties between tip and SAM surfaces under nano scale applied load were measured using an atomic force microscope (AFM) and also those under micro scale applied load were measured using a ball-on-flat type micro-tribotester. Surface roughness and water contact angles were measured with SPM (scanning probe microscope) and contact anglemeter respectively. Results showed that water contact angles of SAMs with the end-group of fluorine show higher relatively than those of hydrogen. SAMs with the end-group of fluorine show lower nano-adhesion but higher micro/nanofriction than those with hydrogen. Water contact angles of SAMs coated by CVD method show high values compared to those by dipping method. SAMs coated by CVD method show the increase of nano-adhesion but the decrease of nano-friction. Nano-adhesion and friction mechanism of SAMs with different end-group was proposed in a view of size of fluorocarbon molecule.

• Restorative Dentistry and Endodontics
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• v.47 no.1
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• pp.13.1-13.13
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• 2022

Objectives: This study evaluated the efficacy of 3 reciprocating systems and the effects of 2 instruments for irrigant activation on filling material removal. Materials and Methods: Forty mesiobuccal roots of maxillary molars were prepared up to size 25.06 and obturated. Micro-computed tomography (micro-CT) examination #1 was performed. Teeth were then divided into 4 groups (n = 10), according to the retreatment protocol: (1) manual, (2) Reciproc Blue, (3) WaveOne Gold, and (4) X1 Blue. Micro-CT examinations #2 and #3 were performed after filling removal and repreparation, respectively. Next, all teeth were divided into 2 new groups (n = 20) according to the irrigant activation protocol: XP Clean (XP Clean size 25.02) and Flatsonic (Flatsonic ultrasonic tip). Micro-CT examination #4 was performed after irrigant activation. Statistical analysis was performed with a significance level set at 5%. Results: WaveOne Gold removed a significantly greater amount of filling material than the manual group (p < 0.05). The time to reach the WL was similar for all reciprocating systems (p > 0.05). X1 Blue was faster than the manual group (p < 0.05). Only manual group improved the filling material removal after the repreparation stage (p < 0.05). Both activation protocols significantly improved the filling material removal (p < 0.05), without differences between them (p > 0.05). Conclusions: None of the tested instruments completely removed the filling material. X1 Blue size 25.06 reached the working length in the shortest time. XP Clean and Flatsonic improved the filling material removal.

• Journal of the Korean GEO-environmental Society
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• v.8 no.6
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• pp.5-12
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• 2007

Mudstone has characteristics that it has high enough strength and stiffness in a dry condition, but the strength and stiffness decrease in a wet condition with groundwater infiltration. The sliding of cut slope frequently encountered in Pohang area has been reported due to the rapid reduction of shear strength in mudstone after being exposed to the air. The study in this paper shows that mudstone having enough strength in a boring stage has lost the strength after installing PRD (percussion rotary drill) steel pipe pile inducing an insufficient bearing capacity. Field test has been performed to investigate the most favorable method for increasing a pile bearing capacity in mudstone with various methods such as MSG (Micro Silica Grouting) around the tip and side of a pile, the perimeter grouting combined with Micro pile reinforcement, and concrete filling after tip reinforcing grouting. MSG has been turned out to be the most favorable method for increasing a pile bearing capacity in mudstone, confirmed by the static load test.

• Journal of Plant Biotechnology
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• v.6 no.2
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• pp.77-85
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• 2004

Development of efficient plant regeneration and genetic transformation protocols (using the Particle Inflow micro-projectile Gun and the shoot-tips as target tissue) of Sorghum bicolor (L.) Moench in terms of expression of the reporter gene, $\beta$-glucuronidase(uidA) is reported here. Two Indian cultivars of sorghum were used in the study, viz. M-35-1 and CSV-15. Plant regeneration was achieved from one-week-old seedling shoot-tip explants via multiple-shoot-clumps and also somatic embryos. The multiple-shoot-clumps were produced on MS medium containing BA (0.5, 1.0 or 2.0 mg/$L^{-1}$), with biweekly subculture. Somatic embryos were directly produced on the enlarged dome shaped expansive structures that developed from shoot-tip explants (without any callus formation) when cultured on MS medium supplemented both with BA (0.5, 1.0 or 2.0 mg/$L^{-1}$) and 2,4-D (0.5 mg/$L^{-1}$). Whereas each multiple-shoot-clump was capable of regenerating more than 80 shoots via an intensive differentiation of both axillary and adventitious shoot buds, the somatic embryos were capable of 90% germination, plant conversion and regeneration. The regenerated shoots could be efficiently rooted on MS medium containing 1.0mg/$L^{-1}$ IBA and successfully transplanted to the glasshouse and grown to maturity with a survival rate of 92%. The plant regeneration efficiency of both the genotypes were similar. After the micro-projectile bombardment, expression of uidA gene was determined by scoring blue transformed cell sectors in the bombarded tissue by an in situ enzyme assay. The optimal conditions comprising a helium pressure of 2200 K Pa, the target distance of 11 cm with helium inlet fully opened and the use of osmoticum have been defined to aid our future strategies of genetic engineering in sorghum with genes for tolerance to biotic and abiotic stresses.