• Transactions of the Korean Society of Mechanical Engineers A
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• v.41 no.3
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• pp.181-186
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• 2017

Single point incremental forming (SPIF) is a sheet-forming technique. It is a die-less sheet metal manufacturing process for rapid prototyping and small batch production. The Critical parameters in the forming process include tool diameter, step depth, feed rate, spindle speed, etc. In this study, these parameters and the die shape corresponding to the Varying Wall Angle Conical Frustum(VWACF) model were used for forming 0.8mm in thick Al5052-O sheets. The Taguchi method of Experiments of Design (DOE) and Grey relational optimization were used to determine the optimum parameters in SPIF. A response study was performed on formability, spring back, and thickness reduction. The research shows that the optimum combination of these parameters that yield best performance of SPIF is as follows: tool diameter, 6mm; spin speed, 60rpm; step depth, 0.3mm; and feed rate, 500mm/min.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.41 no.7
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• pp.673-682
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• 2017

As the culture of making things based on "do-it-yourself" (DIY) activity is increasingly promoted, the use of recent digital technologies and tools, including the 3D printer, have become widespread. However, the use of computerized numerical control (CNC) engraving machine is considered difficult because of the complicated procedures and specialized knowledge required for its operation. Therefore, this study aims to resolve the issue that limits the usability of the CNC engraving machine. This paper presents a novel CNC engraving machine system for non-experts based on human-centered design. First, the size and type of the workpiece and tool are reduced. Second, computer-aided process planning (CAPP) steps such as tool path generation, workpiece clamping, and corresponding coordinate system are automated by compromising productivity and efficiency. As a result, a CNC engraving machine system that can be easily used by non-experts was developed. This development has great significance in that it opens up the possibility of using the CNC engraving machine for a wider range of DIY activities.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.297-297
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• 2011

일반적으로 고출력 반도체 레이저 다이오드는 발진 파장 및 광출력에 따라 다양한 분야에 응용되고 있으며, 특히 발진파장이 808 nm 대역인 고출력 레이저 다이오드의 경우 재료가공, 펌핌용 광원, 의료 분야 등 다양한 응용분야를 가진 광원 중의 하나라고 할 수 있다. 808 nm 대역의 레이저 다이오드 제작에는 현재 InGaAsP/InGaP/GaAs 및 InGaAlAs/GaAs 양자우물을 이용하여 제작되고 있으나 양자우물과 이를 둘러싸는 장벽물질간의 band-offset이 적어 효율적인 고출력 레이저 다이오드의 제작에 다소 어려움이 있기 때문에 강한 캐리어 구속 효과를 지니는 양자점 혹은 양자대쉬 구조를 사용하는 것이 고출력 레이저 다이오드를 제작할 수 있는 한 방법이다. 실험에 사용된 InP/InGaP 양자구조는 Riber사의 compact21 MBE 장치를 사용하여 성장하였으며 GaAs기판을 620-630도에서 가열하여 표면의 산화층을 제거하고 580도에서 약 100 nm 두께의 GaAs 버퍼층 및 50 nm 두께의 InGaP층을 성장하였다. 양자 구조는 MEE (migration enhanced epitaxy) 방식으로 성장되었는데, 이는 InP/InGaP 의 lattice mismatch율이 작아 양자 구조 형성이 어렵기 때문에 InP/InGaP 양자 구조 성장에 적합하다고 생각하였으며, Indium 2초, growth interuption time 10초, phosphorous 2초 그리고 growth interuption time 10초를 하나의 시퀀스로 보고, 그 시퀀스를 반복하여 양자 구조를 성장하였다. 본 실험에 사용된 P 소스는 Riber사의 KPC-250 P-valved cracker모델을 사용하였으며 InP의 성장률은 0.985${\AA}/s$이다. InP/InGaP 양자구조 성장 중에, 성장 온도, 시퀀스 수의 변화 등 다양한 조건을 변화 시켜 샘플을 성장시켰고, 양자 구조 성장을 확인하기 위하여 AFM 및 SEM을 통해 구조적 분석을 하였으며 PL 측정을 통해 광학적 분석을 진행하였다.

• Journal of the Korean Society of Food Science and Nutrition
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• v.24 no.3
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• pp.384-388
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• 1995

High content of polyunsaturated fatty acid in fish oil makes it very susceptible to oxidation, which prevent fish oil from successful application to food processing or functional foods. To resolve this problem, oxidation stability model of fish oil was developed using the following differential equation : $dp/dt=k{\cdot}p(t){\cdot}[P_{max}\;-\;p(t)]$. This differential equation can be intergrated using analytical techniques to give : $p(t)=P_{max}/[1\;+\;[(P_{max}/P_{(0)})\;-\;-1]{\cdot}EXP(-K_p{\cdot}t)]$. At 50, 60, 70 and $80^{\circ}C,\;K_p$ were 0.00535, 0.01345, 0.02516 and 0.04675, respectively. The proposed model was well agreed with the measured data except for some minor deviations. In addition, $K_p$ was expressed as a function of temperature : $K_p=(1/P_{max})EXP\;[1\;-\;(8148/T)+20.1]$. Where T is absolute temperature($^{o}K$).

• Journal of the Korea Institute of Information Security & Cryptology
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• v.30 no.1
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• pp.141-156
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• 2020

Differential privacy, which used to collect and analysis data and preserve data privacy, has been applied widely in data privacy preserving data application. Local differential privacy algorithm which is the local model of differential privacy is used to user who add noise to his data himself with randomized response by self and release his own data. So, user can be preserved his data privacy and data analyst can make a statistical useful data by collected many data. Local differential privacy method has been used by global companies which are Google, Apple and Microsoft to collect and analyze data from users. In this paper, we compare and analyze the local differential privacy methods which used in practically. And then, we study applicability that applying the local differential privacy method in survey or opinion poll scenario in practically.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.4C
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• pp.277-282
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• 2012

In this paper, we present a real-time eye contact system for realistic telepresence using a Kinect depth camera. In order to generate the eye contact image, we capture a pair of color and depth video. Then, the foreground single user is separated from the background. Since the raw depth data includes several types of noises, we perform a joint bilateral filtering method. We apply the discontinuity-adaptive depth filter to the filtered depth map to reduce the disocclusion area. From the color image and the preprocessed depth map, we construct a user mesh model at the virtual viewpoint. The entire system is implemented through GPU-based parallel programming for real-time processing. Experimental results have shown that the proposed eye contact system is efficient in realizing eye contact, providing the realistic telepresence.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.22 no.4
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• pp.299-306
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• 2009

Design optimization is a method to find optimum point which minimizes the objective function while satisfying design constraints. The conventional optimization does not consider the uncertainty originated from modeling or manufacturing process, so optimum point often locates on the boundaries of constraints. Reliability based design optimization includes optimization technique and reliability analysis that calculates the reliability of the system. Reliability analysis can be classified into simulation method, fast probability integration method, and moment-based reliability method. In most generally used MPP based reliability analysis, which is one of fast probability integration method, if many MPP points exist, cost and numerical error can increase in the process of transforming constraints into standard normal distribution space. In this paper, multiplicative decomposition method is used as a reliability analysis for RBDO, and sensitivity analysis is performed to apply gradient based optimization algorithm. To illustrate whole process of RBDO mathematical and engineering examples are illustrated.

• Journal of the Korea Society for Simulation
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• v.20 no.3
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• pp.1-10
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• 2011

In this study, we consider a capacity planning problem where the number of machines at each workstation is determined in manufacturing systems of top-edge electronic products such as semiconductor or display. The considered manufacturing system is the typical hybrid flowshop which has identical parallel machines at each workstation and the setup operation occurs when the types of consecutively processed products are different. The objective of the problem is finding good combinations of the numbers of machines at all workstations, under the given capital amount for purchasing machines. Various heuristic methods for determining the numbers of machines at workstations are proposed and the performances were tested through a series of computational experiments. In the study, a simulation model has been developed in order to simulate the considered manufacturing system with dynamic orders and complex process. The simulation model is also used for conducting the computational comparison test among various proposed methods.

• Journal of Practical Engineering Education
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• v.8 no.2
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• pp.121-128
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• 2016

In injection molding process, the appearance quality issue occurs in most injection molded article. One of thermal designs for the mold was performed by increasing the cavity wall temperature with being as uniform as possible in any position. On the basis of the practical evaluation, the cavity wall temperature and finishing machined cavity surface under the optimum processing conditions are the most significant factors to avoid the appearance issue on the plastic part for a good cosmetic quality. Also, the wrong choice of gate type and location can have a considerable effect on the quality of a molded part and it's so important to keep the correct runner balance from each cavity. We've proposed the education training model of the practical tool technology course for the field oriented education to improve practical tool technology ability and optimized tooling design for injection molding quality which can be performed at the workplace substantially.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.1
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• pp.105-111
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• 2013

The spindle is the main component in machine tools. The static and dynamic characteristics of the spindle directly affect the machining accuracy of workpieces. The characteristics of the spindle depend on the shaft size, bearing span, built-in motor location, and so on. Therefore, the appropriate selection of these parameters is important to improve the spindle characteristics. This paper presents the analysis of the static and dynamic characteristics and optimization design of a 40,000-rpm high-speed spindle. Statistical analysis for optimization and finite element analysis were performed. This study uses the response surface method to optimize the objective function and design factors. The targets are the natural frequency and displacement. The design factors are the shaft length, shaft diameter, bearing span, and motor location. The optimized design provides better results than the initial model, and these results are expected to improve the static and dynamic characteristics of the spindle.