• Journal of the Institute of Electronics and Information Engineers
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• v.53 no.7
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• pp.11-16
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• 2016

Silicon carbide (SiC) has received significant attention over the past decade because of its high-voltage, high-frequency and high-thermal reliability in devices compared to silicon. Especially, a SiC Schottky barrier diode (SBD) is most often used in low-voltage switching and low on-resistance power applications. However, electric field crowding at the contact edge of SBDs induces early breakdown and limits their performance. To overcome this problem, several edge termination techniques have been proposed. This paper proposes an improvement in the breakdown voltage using a double-field-plate structure in SiC SBDs, and we design, simulate, fabricate, and characterize the proposed structure. The measurement results of the proposed structure, demonstrate that the breakdown voltage can be improved by 38% while maintaining its forward characteristics without any change in the size of the anode contact junction region.

• International Journal of Precision Engineering and Manufacturing
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• v.5 no.3
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• pp.35-42
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• 2004

This research describes that the cutting characteristics and tool wear behavior in the micro cutting of three kinds of wear resistant cemented carbides (WC-Co; V40, V50 and V60) using PCD (Poly Crystalline Diamond) and PCBN (Poly crystalline Cubic Boron Nitride) cutting tools by use of the SEM (Scanning Electron Microscope) direct observation method. The purpose of this research is to present reasonable cutting conditions from the viewpoint of high efficient cutting refer to a precise finished surface and tool wear. Summary of the results is as follows: (1) The cutting forces tend to increase as the increase of the weight percentage of WC particles, and the thrust forces was larger than the principal forces in the cutting of WC-Co. These phenomena were different from the ordinary cutting such as cutting of steel or cast iron. (2) The cutting speed hardly influenced the thrust force, because of the frictional force between the cutting tool edge and small WC particles at low cutting speed region such as 2$\mu\textrm{m}$/s. It seemed that the thrust cutting force occurred by the contact between the flank face and work material near the cutting edge. (3) The wear mechanism for PCD tools is abrasion by hard WC particles of the work materials, which leads diamond grain to be detached from the bond. (4) From the SEM direct observation in cutting the WC-Co, it seems that WC particles are broken and come into contact with the tool edge directly. This causes tool wear, resulting in severe tool damage. (5) In the orthogonal micro cutting of WC-Co, the tool wear in the flank face was formed bigger than that in the rake face on orthogonal micro cutting. And the machining surface integrity on the side of the cutting tool with a negative rake angle was better than that with a positive one, as well as burr in the case of using the cutting tool with a negative rake angle was formed very little compared to the that with a positive one.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.2C
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• pp.105-115
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• 2008

The records of field instrumentation, which have been performed on the pneumatic caisson used for substructure of the Youngjong Grand Bridge, were analyzed to investigate the ground contact pressure under rigid foundation of large pneumatic caisson embedded in various ground layers. During sinking the pneumatic caisson, the resisting force was mobilized against sinking the caisson at the contact area between bottom of the caisson and the ground. The resisting force could be measured by the reaction force gauges instrumented under the edge of bottom of the pneumatic caisson. And the ground contact pressure could be estimated by use of the measuring records of the resisting force. The ground contact pressure under rigid foundation of large pneumatic caisson shows concave distribution on bedrock, while convex distribution was shown in marine deposit soil layer as well as weathered rock layer. And, the ground contact pressure in various ground layers was distributed axis-symmetrically. The distribution shape of the ground contact pressure determined by the maximum pressure acting on foundation of the large pneumatic caisson showed good coincidence with the distribution shape proposed for rigid foundation by Kgler(1936) and Fang(1991).

• Journal of Korean Ophthalmic Optics Society
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• v.14 no.3
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• pp.17-27
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• 2009

Purpose: This review article was written to determine the effects of parameters characterizing a hard contact lens (RGP included), such as BCs, diameters, edge angles, on the time interval for tight fitted lens to return to the equilibrium when it was decentered from blinking. Methods: A mathematical formulation was established to relate or calculate the restoring forces and thickness of lacrimal layer beneath the cornea with the various lens parameters when the tight fitted lens was decentered from blinking. Based on this formulation the differential equations and their numerical solution program were set up to describe the time dependence of the lens on the position and to estimate the time for the lens's return to the equilibrium after blink. Results: It is found that the time interval for the tight fitted lens to return to the equilibrium decreases as either the BC decreases or the diameter increases because both the reduction in BC and increase in diameter result in the increase in the lacrimal layer thickness between the lens and cornea increase which yielded the lowering of the viscous friction in the lens motion. As the edge angle of tight fitted lens increases the time for recentering decreases due to the increase in restoring force without change in lacrimal thickness beneath the lens. In the case of flat fitted hard lens (RGP included), the lacrimal layer thickness under the lens increases as either BC or diameter increases which results in reduction in viscous friction so that the time for the lens's return to the equilibrium were to decrease. The edge angle of flat fitted lens does not affect the lens motion. Conclusions: The effect of BCs on the lens motion (time to approach the equilibrium) was concluded to be significant with both tight and flat fitted lens where its results are contrary with each other. The edge angle of lens only affects the motion in tight fitted lenses.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.5 no.6
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• pp.1163-1168
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• 2001

The ranging systems measure range data in three-dimensional coordinate from target surface. These non-contact remote ranging systems is widely used in various automation applications, including military equipment, construction field, navigation, inspection, assembly, and robot vision. The active ranging systems using time of flight technique or light pattern illumination technique are complex and expensive, the passive systems based on stereo or focusing principle are time-consuming. The proposed algorithm, that is based on cross correlation of projection profile of vertical edge, provides advantages of fast and simple operation in the range acquisition. The results of experiment show the effectiveness of the proposed algorithm.

• Progress in Superconductivity
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• v.9 no.2
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• pp.162-166
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• 2008

We are developing a sensitive gamma ray spectrometer based on superconducting transition edge sensors. The detector consists of a small piece of high purity Sn as an absorber and a Ti/Au bilayer as a temperature sensor. It is designed to measure the thermal signal caused by absorption of gamma rays. The mechanical support and the thermal contact between the absorber and the thermometer were made with Stycast epoxy. The bilayer was formed by e-beam evaporation and patterned by wet etching on top of a $SiN_X$ membrane. A sharp superconducting transition of the film was measured near 100 mK. When the film was biased to the edge of the transition, signals were observed due to single photon absorption emitted from an $^{241}Am$ source. The measured spectrum showed several characteristic peaks of the source including 59.5 keV gamma line. The full with at half maximum was about 900 eV for the 59.5 keV gamma line. The background was low enough to resolve low energy lines. Considerations to improve the energy resolution of the gamma ray spectrometer are also discussed.

• Transactions of Materials Processing
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• v.23 no.7
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• pp.439-445
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• 2014

Changes in the accuracy of the geometrical shape after a surface treatment are often very large due to the variation of the deformation mechanisms such as edge draw-in and the variation in springback caused by the reduction in the coefficient of friction between the tool and the blank. In the present study, the resulting shape accuracy due to the changes in deformation is quantitatively examined in order to predict the variation and to remove any undesirable additional tool compensation for the center pillar member made from steel with a UTS of 980MPa. The study examines important process parameters that are closely related with the edge draw-in such as the blank holding force, the contact status between the tool and the blank and the friction coefficient. The proposed method is applied within the finite element analysis of the stamping process for tools after a surface treatment and the amount of edge draw-in and flush values are compared between the analysis and experiments. The results demonstrate that the proposed quantification and finite element scheme are applicable to complicated tool compensation procedures and compensation can be designed effectively.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2002.05a
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• pp.9-12
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• 2002

A parametric study has been conducted to investigate the effect of the geometry on the strength of an unidirectional and fabric hybrid laminated composite joint. Tests are conducted for the specimens with nine different edge-to-hole diameter or width-to-hole diameter ratios. For the finite element analysis, the characteristic length method is used, and the tests for determining the characteristic length are performed additionally. Nonlinear contact problem between the pin and laminate is modeled by the gap element in MSC/NASTRAN. Tsai-Wu failure criteria is applied to the stress on the characteristic curve. The finite element and experimental results shows good agreement in strength of composite joint. Results of the parametric study shows the effect of the geometry is remarkable in the specimens with width-to-hole diameter ratio less than 2.8 and edge-to-hole diameter ratio less than 1.4.

• Tribology and Lubricants
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• v.26 no.5
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• pp.263-271
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• 2010

The rollers of cylindrical roller bearing are axially profiled to relieve high edge stress concentration caused by mainly their finite length and by misalignment. In this paper, a numerical analysis is carried to study the EHL of misaligned (tilted) rollers with axially profiled ends. Using a finite difference method with non-uniform grids and the Newton-Raphson method, the highly nonlinear EHL problems are systematically solved. Physically consistent solutions are obtained for moderate load, material parameters and very small misalignment. For different misalignment angles, contours and sectional plots of pressure and film shape near both edge regions are compared. The asymmetric pressure distributions and film shapes show that the EHL results of finite line contacts are highly dependent upon very small amounts of roller misalignment. Especially, the effect of misalignment on the EHL pressure distribution is much higher than the film shapes.

• Journal of Powder Materials
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• v.3 no.2
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• pp.104-111
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• 1996

In order to obtain homogeneous and high quality products in powder compaction forging process, it is very important to control stress, strain, density and density distributions. Therefore, it is necessary to understand quantitatively the elasto-plastic deformation and densification behaviors of porous metals and metal powders. In this study, elasto-plastic finite element method using Lee-Kim's pressure dependent porous material yield function has been used for the analysis of three dimensional indenting process. The analysis predicts deformed geometry, stress, strain and density distribution and load. The calculated load is in good agreement with experimental one. The calculated results do not show axisymmetric distributions because of the edge effect. The core part which is in contact with the indentor and the outer diagonal edge part are in compressive stress states and the middle part is in tensile stress state. As a results, it can be concluded that three dimensional analysis is more realistic than axisymmetric assumption approach.