• Journal of the Korean Society for Precision Engineering
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• v.24 no.3 s.192
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• pp.134-139
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• 2007

We report the suspension of individual multi-walled carbon nanotubes (MWNTs) from the bottom substrate using deep trench electrodes that were fabricated using optical lithography. During drying of the solution in dielectrophoretic assembly, the capillary force pulls the MWNT toward the bottom substrate, and it then remains as a deformed structure adhering to the bottom substrate after the solution has dried out. Small-diameter MWNTs cannot be suspended using thin electrodes with large gaps, but large-diameter MWNTs can be suspended using thicker electrodes. We present the statistical experimental results for successful suspension, as well as the feasible conditions for a MWNT suspension based on a theoretical approach.

• Journal of the Korean Society of Visualization
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• v.19 no.3
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• pp.15-21
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• 2021

In this study, we investigated the dynamics of a droplet impacting rough hydrophobic surfaces through high-speed imaging. Micrometer-sized structures with grooves and pillars were fabricated on smooth Polydimethylsiloxane (PDMS) surfaces by laser ablation. We used Newtonian and non-Newtonian liquid droplets to study the drop impact dynamics. De-ionized water and aqueous glycerin solutions were used for the Newtonian liquid droplet. The solutions of xanthan gum in water were prepared to provide elastic property to the Newtonian droplet. We found that the orientation of the surface structures affected the maximal spreading diameter of the droplet due to the degree of slippage. During the droplet retraction, the dynamic receding contact angles were measured to be around 90° or less. It resulted in the formation of the micro-capillary bridges between the receding droplet and the surface structures. Then, the rupture of the capillary bridge led to the formation of micrometer-sized droplets on top of the surface structures. The size of the microdroplets was found to increase with increasing the impacting velocity and viscosity of the Newtonian liquid droplets. However, the size of the isolated microdroplets decreased with enhancing the elasticity of the droplets, and the size of the non-Newtonian microdroplets was not affected by the impacting velocity.

• Proceedings of the KSME Conference
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• 2001.06e
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• pp.39-44
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• 2001

The thermocapillary flow in a differentially heated cylindrical liquid bridge under steady rotation of the hot disk is considered in the limit of zero capillary number. Steady flow states and their three-dimensional stability are calculated numerically. A linear stability analysis reveals that the most dangerous perturbations are oscillatory with azimuthal wavenumber m=1 or m=2 depending on the parameters.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2002.10b
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• pp.65-66
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• 2002

One aspect of the stiction problem may be explained by the action of capillary forces in conjunction with surface elasticity. In the present work, the interaction between two elastic half-spaces separated by a small liquid bridge is investigated. By minimizing the total free energy stored in the interface (including elastic energy and surface energy), the equilibrium interface geometry is determined analytically in the case where there is no solid-solid contact. A non-dimensional number, $N_c=299\frac{{\gamma}^2_{LA}cos^2{\theta}V_o}{E^{'2}H^5}$ is found to govern the structure stability. When $N_c{\ge}1$, the two surfaces jump into solid-solid contact and, once this occurs, the contact area will continue to expand until the two surfaces are in full contact.

• Environmental Engineering Research
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• v.18 no.3
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• pp.129-137
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• 2013

The infiltration of rainwater into the surface soil is highly dependent on hydraulic variables, such as the infiltration rate, capillary fringe, moisture content, and unsaturated/saturated hydraulic conductivity. This study estimates the hydraulic conductivity (K) of fluvial deposits at three sites on the right and left banks of Nakdong River in Gyeongbuk Province, South Korea, including the Gumi, Waegwan, and Seongju bridge sites. The K values of 80 samples from 13 boreholes were estimated by using six grain-size methods (Hazen, Slichter, Kozeny, Beyer, Sauerbrei, and Pavchich formulae). The Beyer, Hazen, and Slichter methods showed a better relationship with K values along with an effective grain size than did the other three methods. The grain-size, pumping test, and slug test analyses resulted in different K values, but with similar K values in the grain-size analysis and pumping test. The lower K values of the slug test represent the uppermost fine sand layer.

• Journal of Korean Academy of Oral and Maxillofacial Radiology
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• v.22 no.1
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• pp.43-53
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• 1992

The purpose of this study was to investigate the effects of irradiation on the microvascular structure of the submandibular gland in rats. For this study, 110 male rats were singly irradiated with the dose of 10Gy or 20Gy to their neck region by 6MV X-irradiation and sacrificed on the 1st, 3rd, 7th, 14th and 28th day after irradiation. The author observed distribution and structural changes of the microvasculature in rat submandibular glands using a scanning electron microscope by forming vascular resin casting. The author observed ultrastructural changes of the endothelial cells using a transmission electron microscope, and also histologic changes using a light microscope at Hematoxylin and Eosin staining and PAS staining process. The results of the irradiation effects on the microvasculature in rat submandibular gland were as follows: By light microscopic examination, the dilation of small vessels were observed until the 7th day after irradiation. After then, the vascular constriction and decrease in number of small vessels were noticed. Changes were greater on 20Gy irradiated group than on lOGy irradiated group. The reaction to PAS staining at acinar cells was decreased just after irradiation, but gradually recovered with days. There was no specific difference between two irradiated groups. By scanning electron microscopic examination, general findings on the two irradiated groups were similar. The dilation of conduits and meandering were observed on the 3rd day after irradiation. Decrease of capillary density and blunt ended small vessels were appeared on the 7th day after irradiation. After that, findings of the tortuous and twisted vascular running and coarseness of capillary lumen were increased. Changes were greater on 20Gy irradiated group than on l0Gy irradiated group. By transmission electron microscopic examination, increase of the formation of cytoplasmic process was observed on the 3rd day after irradiation. After that, swelling of endothelial cell and bridge formation of cytoplasmic processes were also observed, but destruction of endothelial cell and loss of basement membrane were observed only on 20Gy irradiated group on the 28th day after irradiation.

• Journal of Sensor Science and Technology
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• v.9 no.2
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• pp.96-105
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• 2000

Fiber optic TR-EFPI(total reflected extrtinsic Fabry-Perot interferometric) sensor was developed to measure the strain of structures, such as building, bridge, aircraft, etc. It has been difficult to distinguish the increase and decrease of the strain from the conventional fiber optic EFPI sensor because their signals only have a sinusoidal wave pattern related to the change of strain. Also, the absolute strain could not be measured by the simple fiber optic EFPI sensor. In this study, in order to measure the magnitude of strain with the direction of strain, the fiber optic sensor was simply constructed with the total reflected EFPI sensor probe. This probe was manufactured with a single mode fiber and a mirror coated fiber in a silica glass capillary tube. The output signal of this fiber optic TR-EFPT sensor can give the information about the magnitude and the direction of strain. The loading-unloading test was performed by the universal testing machine with alluminum beam specimen to compare the strain from fiber optic TR-EFPI sensor with the value from electrical strain gauge. In the result of this experiment. the strain from fiber optic TR-EFPI sensor had a good agreement with the values from the electrical strain gauge.

• Journal of Chest Surgery
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• v.32 no.12
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• pp.1065-1077
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• 1999

Background : Ventricular assist devices(VADs) are being used for patients in postcvardiotomy cardiogenic shock status bridge to cardiac transplant settings and in post-myocardial infarction cardiogenic shock. The VAD which was developed at the Deparment of medical engineering in Dankook University College of Medicine was a pneumatically driven device and can maintain pulsatile flow. The goal of this study is to develop animal experimental models using the VAD and to clarify the reliability and hemodynamic property adequacy of end organ perfusion durability and severity of thrombotic-hemolytic tendency of the device. Material and Method : The pneumatic VAD was applied to 8 adult female lambs, We examined some hemodynamic parameters such as arterial blood pressure pulmonary capillary wedge pressure(pcwp) pulmonary artery pressure(PAP) left atrial pressure hour urine output cardiac index VAD flow EKG to determine the reliability of the VAD and hemodynamic compatibility of the experimental animals within 24 hours of experiment. We also observed the end organ perfusion durability of the VAD and thrombotic-hemolytic property of the VAD after 24 hours of VAD insertion. Result: We could monitor all hemodynamic parameters including pcwp PAP cardiac index EKG, adn hour urine as true clinical settings. We observed that the reliability of the VAD was excellent and the hemodynamic property of the experimental animal and end organ perfusion were adequate within 24 hours of experiment. In four lambs surviving 24 hours after insertion the reliability of the VAD and end organ perfusion were excellent and no thrombotic-hemolytic tendency was noted. However after 15 days of experiment the diaphragm of the VAD was torn and it was recommende that the durability of the VAD should be extended. Conclusion : e conclude that the pneumatic VAD developed at Dankook University Biomedical Engineering has good hemodynamic property and low thromboembolic tendency and presents adequate end organ perfusion but we noted that the durability of the device should be expanded further. It will be possible to do more reliable experiment in the future according to the animal experimental method developed in this study especially with the heart failure models.