• Journal of the Korean Society for Precision Engineering
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• v.13 no.9
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• pp.31-37
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• 1996

This Paper is concerned with effective signal identification method for tool breakage and micro chipping using discrete wavelet transform of feed motor current in milling operations. The wavelet transform uses an analyzing waveletfunction which is localized in both frequency and time domain to detect subtle time localized changes in input signals. The changing pattern of wavelet coefficient is continuously compared to detect tool breakage and micro chipping over one spindle revolution. The results indicate that the wavelet transform can identify tool failure with much greater sensi- tivity than the time domain monitoring and frequency domain monitoring such as FFT. Experimental results are presented to support the proposed scheme.

• Proceedings of the KSME Conference
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• 2008.11b
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• pp.3067-3072
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• 2008

A two-dimensional model for anode-supported IT-SOFCs is proposed in order to accurately consider the heat and mass transport processes with a fully-developed axial velocity profile in channel flow. A comprehensive micro model is employed to describe the electrochemical reaction in anode and cathode of SOFCs. This paper investigates the effects of operational parameters (inlet temperature, the amount of flow rate, and air flow rate) including flow configurations (co-flow and counter-flow) on the current density and temperature distributions in the IT-SOFCs.

• Korean Journal of Materials Research
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• v.19 no.3
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• pp.151-155
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• 2009

Micro-scale copper bumps for build-up PCB were electroplated using a pulse-reverse method. The effects of the current density, pulse-reverse ratio and brightener concentration of the electroplating process were investigated and optimized for suitable performance. The electroplated micro-bumps were characterized using various analytical tools, including an optical microscope, a scanning electron microscope and an atomic force microscope. Surface analysis results showed that the electroplating uniformity was viable in a current density range of 1.4-3.0 A/$dm^2$ at a pulse-reverse ratio of 1. To investigate the brightener concentration on the electroplating properties, the current density value was fixed at 3.0 A/$dm^2$ as a dense microstructure was achieved at this current density. The brightener concentration was varied from 0.05 to 0.3 ml/L to study the effect of the concentration. The optimum concentration for micro-bump electroplating was found to be 0.05 ml/L based on the examination of the electroplating properties of the bump shape, roughness and grain size.

• Proceedings of the KIEE Conference
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• 1996.11a
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• pp.302-304
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• 1996

In this paper, a new algorithm for sensorless speed control of switched reluctance motor (SRM) is proposed. It is based on the measurement of initial rate of change of phase current. The initial rate of rise of phase current mainly depends up on the phase inductance at the time instant when the phase is excited. Therefore, the measurement of initial di/dt permits rotor position estimation, which is used to trigger the next phase. In the proposed technique, there is no need to generate additional current pulses when a phase is not excited. Therefore, this scheme does not introduce the unwanted braking torque. Also, only one current measurement is made every time a phase is excited. This reduces the computational load on the micro-controller and enhances the speed range of the sensorless drive. By using this scheme it is possible to implement the sensorless control of SRM using low cost micro-controller.

• Journal of Biosystems Engineering
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• v.38 no.2
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• pp.113-120
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• 2013

Purpose: Stem cells provide new opportunities in the regenerative medicine for human or animal tissue regeneration. In this study, we report an efficient method for the modulating behaviors of electro-active stem cells by micro-electric current stimulation (mES) without using chemical agents, such as serum or induction chemicals. Methods: Dental pulp stem cells (DPSCs) were cultured on the tissue culture dish in the mES system. To find a suitable mES condition to promote the DPSC functions, the response surface analysis was used. Results: We found that a working micro-current of 38 ${\mu}A$ showed higher DPSC proliferation compared with other working conditions. The mES altered the expressions of intracellular and extracellular proteins compared to those in unstimulated cells. The mES with 38 ${\mu}A$ significantly increased osteogenesis of DPSCs compared with ones without mES. Conclusions: Our findings indicate that mES may induce DPSC proliferation and differentiation, resulting in applying to DPSCs-based human or animal tissue regeneration.

• Proceedings of the Materials Research Society of Korea Conference
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• 2009.11a
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• pp.4.1-4.1
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• 2009

The dream of futurists andtechnologists is to build complex, multifunctional machines so small that theycan only be seen with the aid of a microscope. The unprecedented technologyadvancements in miniaturizing integrated circuits on semiconductors, and theresulting plethora of sophisticated, low cost electronic devices demonstratethe impact that micro/nano scale engineering can have when applied only to thearea of electrical and computer engineering. Emerging research efforts indeveloping organic and inorganic nano materials together with using micro/nanofabrication techniques for implementing integrated multifunctional devices hopeto yield similar revolutions in other engineering fields. By cross linking theindividual engineering fields through micro/nano technology, various organicand inorganic materials and miniaturized system devices can be developed thatwill have future impacts in the IT and life science applications. Yet to buildthe complex micromachines and nanomachine of the future, engineering will needto develop the technology capable of seamlessly integrating these materials andsubsystems together at the micro and nano scales. The micromachines of thefuture will be “integrated nanosystems,” complex devices requiring the integration of multiple materials,phenomena, technologies, and functions at the same platform. To develop thistechnology will require great efforts in materials science and engineering, infundamental and applied sciences. In this talk, we will first discuss thenature of micro and nanotechnology research for IT and life sciences, and thenintroduce selected current activities in micro and nanotechnology research fororganic and inorganic materials and devices. The newly developed micro/nanofabrication processes and devices, combined with in-depth scientificunderstandings of materials, can lead to rapid development of next generationsystems for applications in IT and life sciences.

• Current Photovoltaic Research
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• v.4 no.4
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• pp.140-144
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• 2016

In this paper, core-shell structure of nickel/gold (Ni/Au) conductive layer on poly-methyl-methacrylate (PMMA) micro-ball was fabricated and its conduction property was investigated. Firstly, PMMA micro-ball was synthesized by using dispersion polymerization method. Size of the ball was $2.8{\mu}m$ within ${\pm}7%$ deviation, and appropriate elastic deformation of the PMMA micro-ball ranging from 31 to 39% was achieved under 3 kg pressure. Also, 200 nm thick Ni/Au conductive layer was fabricated on the PMMA micro-ball by uniformly depositing with electroless-plating. Adhesion of the conductive layer was optimized with help of surface pre-treatment, and the layer adhered without peeling-off despite of thermal expansion by collision with accelerated electrons. Composite paste containing core-shell structured particles well cured at low temperature of $130^{\circ}C$ while pressing the test chip onto the substrate to make electrical contact, and electrical resistance of the conductive layer showed stable behavior of about $6.0{\Omega}$. Thus, it was known that core-shell structured particle of the Ni/Au conductive layer on PMMA micro-ball was feasible to flexible electronics.

• Journal of the Korean Society of Combustion
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• v.11 no.2
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• pp.7-14
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• 2006

Catalytic combustion is one of the suitable methods for micro power source due to high energy density and it can be applied to micro structured chamber without consideration of quenching since it is flameless combustion. Catalyst loading in the micro structured combustion chamber is one of the most important issues in the development of micro catalytic combustors. In this research, to coat catalyst on the chamber wall, two methods were investigated. First, $Al_2O_3$ was selected as a support of Pt and $Pt/Al_2O_3$ was synthesized through the alumina sol-gel procedure. To improve the coating thickness and adhesion between catalyst and substrate, heat resistant and water solvable organic-inorganic hybrid binder was used. Porous silicon was also investigated as a catalyst support for platinum. Through the parametric studies of current density and etching time, fabrication process of $1{\sim}2{\mu}m$ of diameter and about $25{\mu}m$ depth pores was confirmed. Coated substrates were test in the micro channel combustor which was fabricated by the wet etching and machining of SUS 304. Using $Pt/Al_2O_3$ coated substrate and Pt coated porous silicon substrate, conversion rate of fuel was over 95 % for $H_2/Air$ premixed gas.

• Korea-Australia Rheology Journal
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• v.19 no.3
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• pp.165-169
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• 2007

The light guide plate (LGP) of LCD-BLU (Liquid Crystal Display-Back Light Unit) is usually manufactured by forming numerous dots by etching process. However, the surface of those etched dots of LGP is very rough due to the characteristics of etching process, so that its light loss is relatively high due to the dispersion of light. Accordingly, there is a limit in raising the luminance of LCD-BLU. In order to overcome the limit of current etched-dot patterned LGP, micro-lens pattern was tested to investigate the possibility of replacing etched pattern in the present study. The micro-lens pattern fabricated by the modified LiGA with thermal reflow process was applied to the optical design of LGP. The attention was paid to the effects of different optical pattern type (i.e. etched dot, micro-lens). Finally, the micro-lens patterned LGP showed better optical qualities than the one made by the etched-dot patterned LGP in luminance.

• 한국태양에너지학회:학술대회논문집
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• 2009.11a
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• pp.104-109
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• 2009

If the Photovoltaic(PV) Module should get physical load, the PV module will be warped according to elongation of the front glass and then micro-crack will be occurred in the heat sealed Solar Cell. This micro-crack drops output of the short circuit current and the open circuit voltage of the PV Module. This is because of increase of resistance component by micro-crack. Micro-crack at specific Solar Cell in the module reduces the durability of PV Module such as less output, Hot-Spot in the PV module caused by Solar Cell output mismatch, heat generating as resistance component caused by micro-crack. In this study, among some factors which effect to the output of crystalline PV Module, we will see how the micro-crack caused by mechanical stress effects to the electrical output of PV Module.