• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.9
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• pp.1277-1284
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• 2000

To enhance heat transfer characteristics of water, micro-encapsulated octadecane of about $10{\mu}m$ diameter was added to water. Viscosity of the slurry was measured by using a capillary tube viscometer. The measured viscosity decreased as the temperature of the slurry increased, and it increased as the fraction of the capsules in the slurry increased. Thermal characteristics of the octadecane were studied by using a differential scanning calorimeter. The melting temperature and the melting energy of the octadecane were found to be $28.6^{\circ}$ and 34.4kcal/kg, respectively. The convective heat transfer characteristics of the slurry were investigated in a flow loop with a constant heat flux test section. Friction factor of the slurry flow was found to be similar to the expected curve by Petukhov. The Nusselt number of the slurry flow was highest when the octadecane melted. Effective thermal capacity of the 14.2% slurry was found to have 1.67 times of the thermal capacity of water.

• Journal of the Korean Society for Precision Engineering
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• v.23 no.9 s.186
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• pp.164-173
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• 2006

The cooling capacity of a micro-heat pipe is mainly governed by the magnitude of capillary pressure induced in the wick structure. For microchannel wicks, a higher capillary pressure is achievable for narrower and deeper channels. In this study, a metallic micro-heat pipe adopting high-aspect-ratio microchannel wicks is fabricated. Micromachining of high-aspect-ratio microchannels is done using the laser-induced wet etching technique in which a focused laser beam irradiates the workpiece placed in a liquid etchant along a desired channel pattern. Because of the direct writing characteristic of the laser-induced wet etching method, no mask is necessary and the fabrication procedure is relatively simple. Deep microchannels of an aspect ratio close to 10 can be readily fabricated with little heat damage of the workpiece. The laser-induced wet etching process for the fabrication of high-aspect-ratio microchannels in 0.5mm thick stainless steel foil is presented in detail. The shape and size variations of microchannels with respect to the process variables, such as laser power, scanning speed, number of scans, and etchant concentration are closely examined. Also, the fabrication of a flat micro-heat pipe based on the high-aspect-ratio microchannels is demonstrated.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2006.05a
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• pp.645-646
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• 2006

Pressure-induced decubitus is a serious disease among the elderly people. Interface pressure occluding vascular perfusion is known to be a cause of decubitus. Therefore, it is essential to quantify the relationship between vascular perfusion and interface pressure among the elderly people. Nine elderly normal people ($57.8{\pm}5.6\;years,\;63.3{\pm}7.0kg,\;1.68{\pm}0.05m$) were participated. Pressure was applied on the ischial tuberosity in the sitting posture from 0mmHg to 135mmHg as capillary vascular perfusion was recorded. The average interface pressure to occlude vascular perfusion under the ischial tuberosity is 120mmHg. Vascular perfusion values at the capillary occlusion is often lower than 60% of the vascular perfusion at 15mmHg. Higher sampling number is required to have more accurate results.

• Journal of Korean Society on Water Environment
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• v.20 no.4
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• pp.370-375
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• 2004

Synthetic organic polyelectrolytes can be used to condition sludges to enhance their dewaterability. When conditioning biological sludges, the charge on the polymer has a significant impact on the effectiveness of the polymer as a conditioner. The objectives of this investigation were to determine the most effective type and dosage of polymer for conditioning digested sludge prior to dewatering, and to investigate the relationship between dewaterability and particle size. 3 types of digested sludge were used under the different digestion processes like anaerobic digestion, aerobic digestion and intermittent aerobic digestion. CST(capillary suction time), TTF(time-to-filter) and SRF(specific resistance to filtration) were tested as a dewaterability index and the number of particle distribution was analyzed using particle size analyzer. The results indicate that cationic polymer appears to be required for effective conditioning of these 3 types digested sludge and the optimal polymer dosage is about 0.6% of SS. CST and TTF are well correlated with mean particle diameter of which the dimension order is 1.7.

• Fibers and Polymers
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• v.6 no.2
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• pp.131-138
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• 2005

A theoretical model is proposed in order to investigate rheological behavior of bubble suspension with large deformation. Theoretical constitutive equations for dilute bubble suspensions are derived by applying a deformation theory of ellipsoidal droplet [1] to a phenomenological suspension theory [2]. The rate of deformation tensor within the bubble and the time evolution of interface tensor are predicted by applying the proposed constitutive equations, which have two free fitting parameters. The transient and steady rheological properties of dilute bubble suspensions are studied for several capillary numbers (Ca) under simple shear flow and uniaxial elongational flow fields. The retraction force of the bubble caused by the interfacial tension increases as bubbles undergo deformation. The transient and steady relative viscosity decreases as Ca increases. The normal stress difference (NSD) under the simple shear has the largest value when Ca is around 1 and the ratio Of the first NSD to the second NSD has the value of 3/4 for large Ca but 2 for small Ca. In the uniaxial elongational flow, the elongational viscosity is three times as large as the shear viscosity like the Newtonian fluid.

• Bulletin of the Korean Chemical Society
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• v.35 no.2
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• pp.539-545
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• 2014

Styrene-acrylamide co-polymer was immobilized on porous partially sub-$2{\mu}m$ silica monolith particles and inner surface of fused silica capillary ($50{\mu}m$ ID and 28 cm length) to result in ${\mu}LC$ and CEC stationary phases, respectively, for separation of anomeric D-glucose derivatives. Reversed addition-fragmentation transfer (RAFT) polymerization was incorporated to induce surface polymerization. Acrylamide was employed to incorporate amide-functionality in the stationary phase. The resultant ${\mu}LC$ and CEC stationary phases were able to separate isomers of D-glucose derivatives with high selectivity and efficiency. The mobile phase of 75/25 (v/v) acetonitrile (ACN)/water with 0.1% TFA, was used for HPLC with a packed column (1 mm ID, 300 mm length). The effects of pH and ACN composition on anomeric separation of D-glucose in CEC have been examined. A mobile phase of 85/15 (v/v) ACN/30 mM sodium acetate pH 6.7 was found the optimized mobile phase for CEC. The CEC stationary phase also gave good separation of other saccharides such as maltotriose and Dextran 1500 (MW~1500) with good separation efficiency (number of theoretical plates ~300,000/m).

• The Korean Journal of Ceramics
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• v.3 no.1
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• pp.5-12
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• 1997

Charged carbon clusters which are formed by the gas activation are suggested to be responsible for the formation of the metastable diamond film. The number of carbon atoms in the cluster that can reverse the stability between diamond and graphite by the capillary effect increases sensitively with increasing the surface energy ratio of graphite to diamond. The gas activation process produces charges such as electrons and ions, which are energetically the strong heterogeneous nucleation sites for the supersaturated carbon vapor, leading to the formation of the charged clusters. Once the carbon clusters are charged, the surface energy of diamond can be reduced by the electrical double layer while that of graphite cannot because diamond is dielectric and graphite is conducting. The unusual phenomena observed in the chemical vapor deposition diamond process can be successfully approached by the charged cluster model. These phenomena include the diamond deposition with the simultaneous graphite etching, which is known as the thermodynamic paradox and the preferential formation of diamond on the convex edge, which is against the well-established concept of the heterogeneous nucleation.

• Korean Chemical Engineering Research
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• v.50 no.4
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• pp.733-737
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• 2012

This study reports the microfluidic preparation of monodisperse multiple emulsions using hydrodynamic control. To generate multiple emulsions, we fabricate a microfluidic capillary device based on co-flowing stream without any surface modification of microchannels. Based on the system, we can successfully generate multiple emulsions (W/O/W) using water containing 0.5 wt% Tween 20, n-hexadecane with 5 wt% Span 80, and 10 wt% poly (vinyl alcohol) (PVA) aqueous solution, respectively. Furthermore, we control the number of inner droplets by modulation of flow rate of inner fluid at fixed flow rate of middle and outer fluid. The multiple emulsions having precisely controlled inner droplets' size and number can be applicable for multiple chemical reactions as an isolated microreactor.

• Archives of Plastic Surgery
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• v.36 no.3
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• pp.254-261
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• 2009

Purpose: The objective of this study was to evaluate the heparin effect for a viability of random - pattern dorsal flap in hairless mouse. Methods: A caudally - based random dorsal flap, measuring $1.5{\times}5cm$, was designed and heparin was applied topically after microneeding. Twenty five male hairless mice were randomly divided into control (Group1, n=5); received only microneedling (Group 2, n=5), only heparin(Group3, n=5), microneedling with saline(Group 4, n=5), and microneedling with heparin group(group5,n=5) to the flap during 7 days. The number of the capillaries were compared between the experimental groups and control group with respect to neovascularization after heparin application using imaging analysis program under hematoxylin - eosin stain. The capillary blood flow was measured by laser Doppler flowmetry. After seven days each animal was evaluated for the percentage area of the flap survival. Mann - Whitnety U test and Kruskal - Wallis statistical analysis of survival relationships was performed. Results: It can be observed increased number of the blood vessels in the experimental groups however it was not statistically significant. Blood flow of the haparin with microneedling group maintained higher than other experimental groups. Treated microneeding and heparin mice were significantly better flap viability than in controls (flap survival 67% and $54.4mm^2$ respectively; p<.01). Positive correlation was shown between flap survival rate and laser Doppler flux value only at first day after surgery. Conclusion: Heparin has a beneficial effect on capillary flow and improve peripheral circulatory disturbances in random pattern flaps.

• Journal of the Korean Society of Food Science and Nutrition
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• v.18 no.2
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• pp.205-210
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• 1989

The influence of triglyceride molecular species on autoxidation was investigated by determining the residual molecular species after incubating soybean oil triglycerides. The molecular species of soybean oil triglycerides were analyzed by capillary column gas chromatography and electron impact ionization mass spectrometry utilizing selected ion monitoring. The autoxidative stability of each molecular species in soybean oil triglycerides appeared to decrease in proportion to the increase in the number of double bonds present in the acyl residues, and it was affected by degree of unsaturation of fatty acid when the number of double bonds in triglyceride were the same. And it appeared to be enhanced by a decreases in the length of the saturated acyl chain present in the glycerides.