• Journal of the Korean Society for Heat Treatment
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• v.22 no.6
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• pp.361-367
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• 2009

The two-step gas nitriding was adopted to increase the depth of surface hardening in 3%Cr-Mo-V steel. The two-step gas nitriding consisted of Step I; $520^{\circ}C{\times}20\;hrs$ and Step II; $550^{\circ}{\times}70\;hrs$. The layer of two-step gas nitriding showed better uniformity and deeper nitriding layer than one-step gas-nitriding layer. The maximum surface hardness showed the value of 850 Hv. The maximum depth of nitrogen permeation showed $750\;{\mu}m$ (350 Hv). X-ray diffraction analysis showed that compound layer was mainly consisted of CrN and $\varepsilon-Fe_3N$ phases. These phases were presumed contributing to surface hardening and wear resistance. However, the corrosion resistance of gas-nitrided Cr-Mo-V steel were not improved in the solution of 1 N HCl and NaOH. Therefore, it is necessary that the continuous study for improvement of corrosion resistance hereafter.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1997.04a
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• pp.1063-1067
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• 1997

A study of carbide step drill cutting ability is highly progessing the step drill with more then twice diameter rate is so difficult in regrinding and very easy to damage during machining. As the machining of step drill for closed hole is occur to breakage at small diamter poistion, so it is very difficult to machinine. Thue, in this experiment, We investance roundness and surface roghness by machining distance and were identifid that the first distance, 5~10m, was fine with 7 .mu.m but the arround of 15m was happened so much alternation. And we were indentified that after 20m was happend statable machining. The surface roughness was happened the same conditions. So application of stwp drill we think that the selection of cutting conditions need lots consideration and the study of step drill's diameter ratio ratio is carred out.

• Journal of Biomedical Engineering Research
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• v.26 no.2
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• pp.73-86
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• 2005

We need to flatten the brain cortex to smooth surface, sphere, or 2D plane in order to view the buried sulci. The rendered 3D surface of the segmented white matter and gray matter does not have the topology of a sphere due to the partial volume effect and segmentation error. A surface without correct topology may lead to incorrect interpretation of local structural relationships and prevent cortical unfolding. Although some algorithms try to correct topology, they require heavy computation and fail to follow the deep and narrow sulci. This paper proposes a method that corrects topology of the rendered surface fast, accurately, and automatically. The proposed method removes fractions beside the main surface, fills cavities in the inside of the main surface, and removes handles in the surface. The proposed method to remove handles has three-step approach. Step 1 performs smoothing operation on the rendered surface. In Step 2, vertices of sphere are gradually deformed to the smoothed surfaces and finally to the boundary of the segmented white matter and gray matter. The Step 2 uses multi-resolutional approach to prevent the deep sulci from geometrical intersection. In Step 3, 3D binary image is constructed from the deformed sphere of Step 2 and 3D surface is regenerated from the 3D binary image to remove intersection that may happen. The experimental results show that the topology is corrected while principle sulci and gyri are preserved and the computation amount is acceptable.

• Korean Journal of Computational Design and Engineering
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• v.3 no.2
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• pp.87-102
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• 1998

Given a sequence of cross-sectional curves, the skinning method generates a freeform surface that interpolates the given curves in that sequence. This thesis presents a construction method of a B-spline skinning surface that is fair and satisfies volume constraints. The fairness metric is based on the parametric energy functional of a surface. The degrees of freedom in surface control are closely related lo control points in the skinning direction. The algorithm fur finding a skinning surface consists of two step. In the first step, an initial fair surface is generated without volume constraints and one coordinate of each control point is fixed. In the second step, a final surface that meets all constraints is constucted by rearranging the other coordinates of each control point that defines the initial surface A variational Lagrange optimization method produces a system of nonlinear equations, which can be solved numerically. Moreover, the reparametrization of given sectional curves is important for the construction of a reasonable skinning surface. This thesis also presents an intuitive metric for reparametrization and gives some examples that are optimized with respect to that metric.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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• pp.547-552
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• 2003

In mold machining, there are many concave machining regions where chatter and tool deflection occur since MRR (material removal rate) increases as curvature increases even though cutting speed and depth of cut are constant. Boolean operation between stock and tool model is widely used to compute MRR in NC milling simulation. In finish cutting, the side step is reduced to about 0.3mm and tool path length is sometimes over 300m. so Boolean operation takes long computation time and includes much error if the resolution of stock and tool model is larger than the side step. In this paper, curvature of CL(cutter location) surface and side step of tool path is used to compute the feedrate for constant MRR machining. The data structure of CL surface is Z-map generated from NC tool path. The algorithm to get local curvature from discrete data was developed and applied to compute local curvature of CL surface. The side step of tool path was computed by point density map which includes cutter location point density at each grid element. The feedrate computed from curvature and side step is inserted to new tool path to regulate MRR. The resultants wire applied to feedrate optimization system which generates new tool path with feedrate from NC codes for finish cutting. The system was applied to speaker mold machining. The finishing time was reduced to 12.6%. tool wear was reduced from 2mm to 1.1mm and chatter marks and over cut on corner were removed.

• Carbon letters
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• v.3 no.4
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• pp.219-225
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• 2002

The two-step surface modifications of activated carbon was carried out to improve the adsorption capacity of toxic heavy metal ions in liquid phase. Physical and chemical properties of the as-received activated carbon (AC) and two kinds of surface-modified activated carbons ($1^{st}AC$ and $2^{nd}AC$) were evaluated through the BET analysis, surface acidity, and oxides measurements. Specific surface area and pore volume did not significantly change, but surface oxide-group remarkably increased by the surface modification. Equilibrium and batch adsorptions of the various metals, such as Pb, Cd, and Cr, using AC, $1^{st}AC$, and $2^{nd}AC$ were performed at initial pH 5. The adsorption capacity and rate of $2^{nd}AC$ were higher than those of AC and $1^{st}AC$. The carboxylic/sodium carboxylate complex groups were developed from the two-step surface modification of activated carbon, which strongly affected the adsorption of metal ions.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.13 no.2
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• pp.177-182
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• 2000

Composite insulation system of liquid nitrogen and solid spacer is widely applied in high temperature superconduction power machine. This study has three step procedure. As follow, first step is composition of parallel deposited electrode and vertically deposited electrode along the direction of immersion in liquid nitrogen(LN2). Second step is investigation into surface flashover voltage of solid spacer under partially immersed in LN2, and last step is comparison the result of this research with that of fully immersed in LN2 and at cryogenic temperature gaseous nitrogen(GN2). This result presented that surface flashover voltage along solid spacer half immersed in LN2 was almost the same as that of fully immersed spacer when the thickness of spacer(t) was t<10mm. In the case of t> 10mm, however, spacer flashover voltage was equal to that obtained in GN2 at cryogenic temperature. And the immersed direction functions as role of deciding the difference of surface flashover voltage.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2001.10a
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• pp.93-100
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• 2001

The three dimensional(3D) reconstruction from two dimensional(2D) image data is using in many fields such as RPD(Rapid Product Development) and reverse engineering. In this paper, the main step of 3D reconstruction is comprised of two steps : image processing step and B-spline surface approximation step. In the image processing step, feature points of each cross-section are obtained by means of several image processing technologies. In the B-spline surface approximation step, using the data of feature points obtained in the image processing step, the control points of B-spline surface are obtained, which are used for IGES file of 3D CAD model.

• Journal of Korean Society for Quality Management
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• v.42 no.4
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• pp.685-700
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• 2014

Purpose: The purpose of this paper is to develop a systematic weighting procedure based on process capability indices method applying weighted mean squared error minimization (WMSE) approach to dual response surface optimization. Methods: The proposed procedure consists of 5 steps. Step 1 is to prepare the alternative vectors. Step 2 is to rank the vectors based on process capability indices in a pairwise manner. Step 3 is to transform the pairwise rankings into the inequalities between the corresponding WMSE values. Step 4 is to obtain the weight value by calculating the inequalities. Or, step 5 is to obtain the weight value by minimizing the total violation amount, in case there is no weight value in step 4. Results: The typical 4 process capability indices, namely, $C_p$, $C_{pk}$, $C_{pm}$, $C_{pmk}$ are utilized for the proposed procedure. Conclusion: The proposed procedure can provide a weight value in WMSE based on the objective quality performance criteria, not on the decision maker's subjective judgments or experiences.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.25 no.6
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• pp.108-114
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• 2011

In order to mitigate the possible hazards from electric shock due to the touch and step voltages, the high resistivity material such as gravel is often spread on the earth's surface in substations. When the grounding electrode is installed in two-layer soil structures, the surface layer soil resistivity is different with the resistivity of the soil contacted with the grounding electrodes. The design of large-sized grounding systems is fundamentally based on assuring safety from dangerous voltages within a grounding grid area. The performance of the grounding system is evaluated by tolerable touch and step voltages. Since the floor surface conditions near equipment to be grounded are changed after a grounding system has been constructed, it may be difficult to determine the tolerable touch and step voltage criteria. In this paper, to propose an accurate and convenient method for evaluating the protective performance of grounding systems, the propriety of the method for evaluating the current flowing through the human body around on a counterpoise buried in two-layer soils is presented. As a result, it is reasonable that the grounding system performance would be evaluated by measuring and analyzing the current flowing through the human body based on dangerous voltages such as the touch or step voltages and the contact resistance between the ground surface and feet.