• The Korean Journal of Ceramics
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• v.6 no.3
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• pp.291-295
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• 2000

The pyroelectric property of $Pb_{0.9}La$_{0.1}TiO_3$ceramics in a range of 1.3-4.1$\mu\textrm{m}$, fabricated by conventional solid sintering, was investigated as a function of poling field. The pyroelectric of the 4.1$\mu\textrm{m}$ of $Pb_{0.9}La$_{0.1}TiO_3$ceramics is higher than that of the 1.3$\mu\textrm{m}$ and 1.7$\mu\textrm{m}$ of $Pb_{0.9}La$_{0.1}TiO_3$ceramics at a low poling field and the pyroelectric coefficient is 25nC/$\textrm{cm}^2$K at a 4kV/mm poling field in every grain size. In order to explain this phenomenon, the intrinsic and extrinsic effects in view of the definition of the pyroelectric coefficient are introduced. The intrinsic and extrinsic effects on the pyroelectric property were investigated by measuring the tetragonal ratio and the $I_{002}$ with temperature with high temperature X-ray diffractometer. The change of spontaneous polarization and the $90^{\circ}$domain wall motion with temperature in the 1.3$\mu\textrm{m}$ and 4.2$\mu\textrm{m}$ of $Pb_{0.9}La$_{0.1}TiO_3$ceramics have no effects on the pyroelectric coefficient. In our study, it can be seen that the pyroelectric coefficient is related to the quantity of $180^{\circ}$domain switching after poling treatment.

• Smart Structures and Systems
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• v.9 no.5
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• pp.393-410
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• 2012

Conventional geotechnical instrumentation techniques available for monitoring of slopes, especially soil-nailed slopes have limitations such as electromagnetic interference, low accuracy, poor longterm reliability and difficulty in mounting a series of strain sensors on a soil nail bar with a small-diameter. This paper presents a slope monitoring system based on fibre Bragg grating (FBG) sensing technology. This monitoring system is designed to perform long-term monitoring of slope movements, strains along soil nails, and other slope reinforcement elements. All these FBG sensors are fabricated and calibrated in laboratory and a trial of this monitoring system has been successfully conducted on a roadside slope in Hong Kong. As part of the slope stability improvement works, soil nails and a toe support soldier-pile wall were constructed. During the slope works, more than 100 FBG sensors were installed on a soil nail, a soldier pile, and an in- place inclinometer. The paper presents the layout and arrangement of the instruments as well as the installation procedures adopted. Monitoring data have been collected since March 2008. This trial has demonstrated the great potential of the optical fibre monitoring system for long-term monitoring of slope performance. The advantages of the slope monitoring system and experience gained in the field implementation are also discussed in the paper.

• Journal of the Korean institute of surface engineering
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• v.43 no.1
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• pp.25-30
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• 2010

Titanium and titanium alloys are widely used for orthopedic and dental implants for their superior mechanical properties, low modulus, excellent corrosion resistance and good biocompatibility. In this study, corrosion behaviors of nanotube formed on the bone plate of Ti-6Al-4V alloy for dental use have been investigated. $TiO_2$ nanotubes were formed on the dental bone plates by anodization in $H_3PO_4$ containing 0.6 wt % NaF solution at $25^{\circ}C$. Electrochemical experiments were performed using a conventional three-electrode configuration with a platinum counter electrode and a saturated calomel reference electrode. Anodization was carried out using a scanning potentiostat (EG&G Co, Model 263A USA), and all experiments were conducted at room temperature. The surface morphology was observed using field emission scanning electron microscopy (FE-SEM) and energy dispersive x-ray spectroscopy(EDS). The corrosion behavior of the dental bone plates was examined using potentiodynamic test(potential range of -1500~2000 mV) in a 0.9% NaCl solution by potentiostat (EG&G Co, PARSTAT 2273. USA). The inner diameter of nanotube was about 150~180 nm with wall thickness of about 20 nm. The interspace of nanotube to nanotube was 50 nm. The passive region of the nanotube formed bone plates showed the broad range compared to non-nanotube formed bone plates. The corrosion surface of sample was covered with corrosion products.

• International Journal of Air-Conditioning and Refrigeration
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• v.13 no.1
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• pp.51-60
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• 2005

This paper reviews the studies on the pressure drop and the heat transfer in microchannels. Although a lot of studies about the single-phase flow have been done until now, conflicting results are occasionally reported about flow transition from laminar flow to turbulent flow, friction factor, and Nusselt number. Some studies reported the early flow transition due to relatively greater wall effect like surface roughness, but the other studies showed that the flow transition occurred at the Reynolds number of about 2300 and the early flow transition might be due to less accurate measurement of the channel geometry. Also, there have been arguments whether the conventional relation based upon continuum theory can be applied to the fluid flow and the heat transfer in microchannels without modification or not. The studies about the two-phase flow in microchannels have been mostly about investigating the flow pattern and the pressure drop in rectangular channels using two-component, two-phase flow like air/water mixture. Some studies proposed correlations to predict two-phase flow pressure drop in microchannels. They were mostly based on Lockhart-Martinelli model with modification on C-coefficient, which was dependent on channel geometry, Reynolds number, surface tension, and so on. Others investigated the characteristics of flow boiling heat transfer in microchannels with respect to test parameters such as mass flux, heat flux, system pressure, and so on. The existing studies have not been fully satisfactory in providing consistent results about the pressure drop and the heat transfer in microchannels. Therefore, more in-depth studies should be done for understanding the fundamentals of the transport phenomena in the microchannels and giving the basic guidelines to design the micro devices.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 1999.10a
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• pp.33-33
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• 1999

The Coanda effect is the tendency for a fluid jet to atach itself to an adjacent surface and follow its contour without causing an appreciable flow separation. The jet is pulled onto the surface by the low pressure region which develops as entrainment pumps fluid from the region between the jet and the surface. Then the jet is held to the wall surface by the resulting radial pressure gradient which balance the inertial resistance of the jet to turning. The jet may attach to the surface and may be deflected through more than 180 dog, when the radius of the Coanda surface is sufficiently large compared to the height of the exhaust nozzle. However, if the radius of curvature is small, the jet turns through a smaller angle, or may not attach to the surface at all. In general, the limitations in size and weight of a device will limit the radius of the deflection surface. Thus much effort has been paid to improve the jet deflection in a variety of engineering fields. The Coanda effect has long been applied to improve aerodynamic characteristics, such as the drag/lift ratio of flight body, the engine exhaust plume thrust vectoring, and the aerofoil/wing circulation control. During the energy crisis of the seventies, the Coanda jet was applied to reduce vehicle drag and led to drag reductions of as much as about 30% for a trailer configuration. Recently a variety of industrial applications are exploiting another characteristics of the Coanda jets, mainly the enhanced turbulence levels and entrainment compared with conventional jet flows. Various industrial burners and combustors are based upon this principle. If the curvature of the Coanda surface is too great or the operating pressure too high, the jet flow will break away completely from the surface. This could have catastrophic consequences for a burner or combustor. Detailed understanding of the Coanda jet flow is essential to refine the design to maximize the enhanced entrainment in these applications.

• Imaging Science in Dentistry
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• v.42 no.4
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• pp.243-247
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• 2012

Purpose: This study was performed to compare the inverted digital images and film-based images of dry pig mandibles to measure the periodontal bone defect depth. Materials and Methods: Forty 2-wall bone defects were made in the proximal region of the premolar in the dry pig mandibles. The digital and conventional radiographs were taken using a Schick sensor and Kodak F-speed intraoral film. Image manipulation (inversion) was performed using Adobe Photoshop 7.0 software. Four trained examiners made all of the radiographic measurements in millimeters a total of three times from the cementoenamel junction to the most apical extension of the bone loss with both types of images: inverted digital and film. The measurements were also made in dry mandibles using a periodontal probe and digital caliper. The Student's t-test was used to compare the depth measurements obtained from the two types of images and direct visual measurement in the dry mandibles. A significance level of 0.05 for a 95% confidence interval was used for each comparison. Results: There was a significant difference between depth measurements in the inverted digital images and direct visual measurements (p>|t|=0.0039), with means of 6.29 mm ($IC_{95%}$:6.04-6.54) and 6.79 mm ($IC_{95%}$:6.45-7.11), respectively. There was a non-significant difference between the film-based radiographs and direct visual measurements (p>|t|=0.4950), with means of 6.64mm($IC_{95%}$:6.40-6.89) and 6.79mm($IC_{95%}$:6.45-7.11), respectively. Conclusion: The periodontal bone defect measurements in the inverted digital images were inferior to film-based radiographs, underestimating the amount of bone loss.

• Journal of the korean academy of Pediatric Dentistry
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• v.39 no.2
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• pp.192-198
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• 2012

Revascularization of the pulp in a necrotic, infected immature tooth with apical periodontitis was attempting several years. Revascularization of partially necrotic pulp in an immature tooth is based on the concept that vital dental stem cells can survive pulpal necrosis. Revascularization procedure obtains longer and thicker roots in teeth with necrotic pulp diagnosis. Pulp revascularization for immature permanent molars can be possibly applied on cases having difficulty to use conventional root canal treatment due to abnormally thin root canal wall or severe root curvature. Also, when an uncooperative patient does not agree with sedative treatment the revascularization can be useful. And a patient with disability who is barely cooperative can be another indication of this treatment. In this case report, pulp revascularization using triple-antibiotics, metronidazole, ciprofloxacine and minocycline, was applied on the immature first permanent molar infected by caries.

• Journal of IKEEE
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• v.18 no.2
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• pp.214-219
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• 2014

In this paper, the usage of tilt-implanted trench Schottky diode(TITSD) based on silicon carbide is proposed. A tilt-implanted trench termination technique modified for SiC is proposed as a method to keep all the potentials confined in the trench insulator when reverse blocking mode is operated. With the side wall doping concentration of $1{\times}10^{19}cm^{-3}$ nitrogen, the termination area of the TITSD is reduced without any sacrifice in breakdown voltage while potential is confined within insulator. When the trench depth is set to 11um and the width is optimized, a breakdown voltage of 2750V is obtained and termination area is 38.7% smaller than that of other devices which use guard rings for the same breakdown voltage. A Sentaurus device simulator is used to analyze the characteristics of the TITSD. The performance of the TITSD is compared to the conventional trench Schottky diode.

• Proceedings of the Korean Geotechical Society Conference
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• 2009.09a
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• pp.815-826
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• 2009

The paper presents a case study addressing the design and construction aspects for DCM(Deep Cement Mixing) method employed as the foundation of a caisson type breakwater with heavy weight(10,700 ton/EA) and a high design wave height($H_{1/3}$=8.7m). The DCM was designed for the project(Ulsan New Port North Breakwater Phase 1) by optimizing the pattern of DCM columns with a combination of short and long columns (i.e., block type(upper 3m)+wall type(lower)) and considering overlapped section between columns as a critical section against shear force where the coefficient of effective width of treated column($\alpha$) was estimated with caution. It was shown that the value can be 0.9 under the condition with the overlapped width of 30cm. In addition to that, a field trial test was performed after improving conventional DCM equipment (e.g., mixing blades, cement paste supplying pipes, multi auger motor, etc.) to establish a standardized DCM construction cycle (withdrawal rate of mixing blades) which can provide the prescribed strength. The result of the field strength test for cored DCM specimens shows that the averaged strength is larger than the target strength and the distribution of the strength(with a defect rate of 7%) also satisfies with the quality control normal distribution curve which allows defect rate of 15.9%.

• Journal of the Society of Naval Architects of Korea
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• v.35 no.4
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• pp.1-10
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• 1998

This paper presents a vorticity-based numerical method for analyzing an incompressible Newtonian viscous flow around an impulsively started cylinder. The Navier-Stockes equations have a natural Helmholtz decomposition. The vorticity transport equation and the pressure equation are derived from this decoupled form. The associated boundary conditions are dynamic for the vorticity and pressure variables representing the coupling relation between them and the force balance on the wall. The various numerical treatments for solving the governing equations are introduced. According to Wu et al.(1994), the boundary conditions are decoupled, keeping the dynamic relation between vorticity and pressure. The vorticity transport equation is formulated by FVM and TVD(Total Variation Diminishing) scheme is used for the convection term. An integral approach similar to the panel method is used to obtain the velocity field for a given vorticity field and the pressure field, instead of the conventional differential approaches. In the numerical process, the structured grid is generated. The results are compared to existing numerical and analytic results for the validity of the present method.