• 한국전산유체공학회:학술대회논문집
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• 2011.05a
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• pp.387-391
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• 2011

Since MEMS based micro actuators or generating devices have high efficiency per volume, plenty of research are ongoing. Among them, MEMS based millimeter-scale micro gas' turbine is one of the most powerful issue for replacing chemical batteries. However, since limiting of MEMS manufacturing technique, it is very difficult that makes wide turbine bearing area. It causes low DN number, so sufficient bearing force is hard to achieve. Thus, the most important issue on micro gas turbine is proper bearing design which can keep rotor stable during operation. In order to that, micro-scale gas-lubricated bearing is generally used. In this paper, basic feasibility study and design of journal bearing for 10mm diameter micro gas turbine is described Journal bearing is hydrostatic gas-lubricated type. Numerical simulation is performed with ANSYS CFX 11.0 which is commercial numerical tool. Repulsive force when there is radial displacement in bearing and returning time is calculated using steady and unsteady cases. Auto re-meshing technic is used for moving mesh unsteady cases which simulate displacement of axis and its movement. The simulation results are used for further design of micro gas turbine, and experiment will be done later.

• The korean journal of orthodontics
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• v.51 no.4
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• pp.282-292
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• 2021

Objective: To quantitatively analyze the effect of nicotine on orthodontic tooth movement (OTM) and bone remodeling in rats using micro-computed tomography and tartrate-resistant acid phosphatase immunostaining. Methods: Thirty-nine adult male Sprague-Dawley rats were randomized into three groups: group A, 0.5 mL normal saline (n = 9, 3 per 3, 7, and 14 days); group B, 0.83 mg/kg nicotine (n = 15, 5 per 3, 7, and 14 days); and group C, 1.67 mg/kg nicotine (n = 15, 5 per 3, 7, and 14 days). Each animal received daily intraperitoneal injections of nicotine/saline from the day of insertion of identical 30-g orthodontic force delivery systems. A 5-mm nickel-titanium closed-coil spring was applied between the left maxillary first molar (M1) and the two splinted incisors. The rate of OTM and volumetric bone changes were measured using micro-computed tomography. Osteoclasts were counted on the mesial alveolar bone surface of the distobuccal root of M1. Six dependent outcome variables, including the intermolar distance, bone volume fraction, bone mineral density, trabecular thickness, trabecular volume, and osteoclast number, were summarized using simple descriptive statistics. Nonparametric Kruskal-Wallis tests were used to evaluate differences among groups at 3, 7, and 14 days of OTM. Results: All six dependent outcome variables showed no statistically significant among group-differences at 3, 7, and 14 days. Conclusions: The findings of this study suggest that nicotine does not affect OTM and bone remodeling, although fluctuations during the different stages of OTM in the nicotine groups should be elucidated in further prospective studies.

• Journal of the Korean Society of Visualization
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• v.10 no.1
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• pp.40-46
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• 2012

Recently micro shock tube is extensively being used in many diverse fields of engineering applications but the detailed flow physics involved in it is hardly known due to high Knudsen number and strong compressibility effects. Unlike the macro shock tube, the surface area to volume ratio for a micro shock tube is very large. This unique effect brings many complexities into the flow physics that makes the micro shock tube different compared with the macro shock tube. In micro shock tube, the inter- molecular forces of working gas can play an important role in specifying the flow characteristics of the unsteady shock wave flow which is essentially generated in all kinds of shock tubes. In the present study, a CFD method was used to predict and visualize the unsteady shock wave flows using the unsteady compressible Navier-Stokes equations, furnished with the no-slip and slip wall boundary conditions. Maxwell's slip equations were used to mathematically model the shock movement at high Knudsen number. The present CFD results show that the propagation speed of the shock wave is directly proportional to the initial pressure and diameter of micro shock tube.

• Journal of Biomedical Engineering Research
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• v.28 no.1
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• pp.102-107
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• 2007

In molecular imaging studies via magnetic resonance imaging, in vivo cell tracking is an important issue for the observation of cell therapy or disease behavior. High resolution imaging and longitudinal study are necessary to track the cell movement. Since the field inhomogeneity extends over several voxels, we have performed the numerical analysis using the sub-voxel method dividing a voxel of MR image into several elements and the information about the field inhomogeneity distribution around the micro-beads. We imbedded ferrite-composite micro-beads with the size of $20-150{\mu}m$ in the subject substituted for cells to induce local field distortion. In the phantom imaging with the isotropic voxel size of $200{\mu}m^3$, we could confirm the feasibility of sub-voxel tracking in a 3.0 T MRI.

• Proceedings of the KSR Conference
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• 2004.06a
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• pp.632-637
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• 2004

In the shrink or press fitted shaft such as railway axle, fretting can occur by cyclic stress and micro-slippage due to local movement between the shaft and the hub. When the fretting occurs in the press fitted shaft, the fatigue strength remarkably decreases compared with that of without fretting. In this paper, the analysis of contact stresses in a press fitted shaft in contact with a hub was conducted by finite element method and the micro-slip according to the bending load was analyzed. It is found that the largest stress concentration and maximum slip amplitude of shrink fitted shaft are found at the edge of the interface and the distribution of contact stresses at the contact edge has largely influenced and coefficient of friction.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.5 no.2
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• pp.85-93
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• 1993

The rise of a large gas bubble or slug in a Micro Two-Phase Closed Thermosyphon with a thin wire insert has been analiged by the potential flow theory. The effect of the interfacial surface tension is explicitly accounted by application of the Kelvin-Laplace equation and solved for the bubble shape. The solution is expressed in terms of the Stokes stream function which consists of an infinite series of Bessel functions. The conditions of the bubble movement in a Micro Two-Phase Closed Thermosyphon were theoretically ascertained.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2000.11a
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• pp.922-925
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• 2000

As mechanical components require size minimization and high precision, micro die machining technology has been developed in many fields. to machine a micro die by EDM, sometimes, a polygonal electrode is use. Machining corners by MEDM shows special characteristics. Physically, electrons are concentrated in sharp region and a high potential level is established in this region. Also, the electrode can't be rotated when machining a polygonal cavity, and machined debris can not drawn off easily. Discharge concentration in corners and 2nd discharge by machined debris result in distortion of corner shape. This phenomena can be improved by shaking the electrode. This method is also shown to be effective in improving surface roughness by circulation of machining fluid resulting from movement of the electrode.

• Journal of Welding and Joining
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• v.29 no.1
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• pp.115-122
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• 2011

This study is to propose an in-process monitoring system for micro resistance spot welding processes using minute accelerometer. A minute accelerometer is mounted on the upper moving electrode tip holder. With its high sensitivity and frequency response characteristics, accelerometer output signal has been successfully recorded and integrated twice to reflect electrode expansion during micro spot welding processes. The analysis of electrode expansion pattern was attempted to find its correlation with spot weld quality. Major previous findings1-6) regarding spot weld quality assessment with the electrode expansion signal in large scale resistance spot welding processes were proved to be true in this in-process monitoring system.

• Korean Journal of Culture and Social Issue
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• v.12 no.2
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• pp.101-114
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• 2006

This study was examined the effective nonverbal behavior cues of detecting suspects' lies in the investigation scene. In order to search the suspects who drank the alcohol liquor without a permission, 18 soldiers were interviewed. 8 solders had drunken alcohol and had lied when was asked(lie group). The other 10 soldiers hadn't drunken alcohol and had told the truth(truth group). The mean frequencies of nonverbal behaviors were compared lie group with truth group. The following behaviors were measured by frequency: vocal characteristics (high pitch of voice, speech hesitations, speech error, frequency of pauses, period of pauses, latency period), facial characteristics (gaze, smile, touching face, blinking, facial micro-expression), body movement (illustrators, hand and finger movement, leg and foot movement, head movement, trunk movement, shifting position). As results, this study found that deception cues were periods and frequencies of pause, micro-expression, head movements. The lie group had less periods and frequencies of pause, and more micro-expression, head movements than truth group. But, this study didn't found Othello's error cues.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.272-273
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• 2013

Some living thingsuse micro- or nano- structures for living in nature. Scientists and engineers made efforts to mimic them, and they succeeded in making new types of applications. They used 'Namib desert beetle' to self-filling device by moisture harvesting and 'lotus leaf' to self-cleaning device by water repelling. 'Namib desert beetle' and lotus leaf have micro-patterns on their surface, which consists of hydrophobic or hydrophilic materials [1]. Moreover, micro-patterns on the surface make self-filling or self-cleaning property enhanced because of the surface roughness. Surface roughness enhances wettability [2]. Micro-pattern is a significant factor to make the surface be functional, so we want to make new types of functional surface by micro-patterning. In this work,we make several functional micro-patterns (radial, line, and dot arrays) using maskless lithography and analyze the characteristics of each micro-pattern. In order to analyze and understand surface characteristics, micro-patterns with varying sizes are investigated. All experiments are proceeded on mr-DWL5 photo resists coated on silicon wafers in same condition. All the experiments have demonstrated good performances about hydrophobic or hydrophilic property corresponding to their material and structural combinations. In radial micro-pattern, although the surface is flat, water drops on hydrophilic radial pattern can be convergent to a middle point and water drops on hydrophobic radial pattern can be divergent from the middle point. In line array micro-pattern, water drops can roll off along only one direction in parallel with the line arrays. Such phenomena might be mainly caused by the local change of surface roughness. From these results, controlling the movement and direction of water drops is made feasible without introducing a slope, which can potentially be used for new types of applications.