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Compensation of image noise induced by difference in optical characteristics of array-LED chips of LED print head

Science China(Technological Sciences) 2017年第12期60卷 1819-1830页

作者： kim Wan-Chin PARK Yong-Shik kim Sung-dae LIM Jiseok Department of Automotive Engineering Honam University Gwansan-gu Gwangju 62399 Korea Mangoslab Co. Ltd. Startupeampus 20 Pangyo-ro 289beon-gil Bundang-gu Seongnam-si Gyeonggi-do 13488 Korea S-Printing Solution Co. Ltd. (Samsung Electronics Ltd) Suwon Gyeonggi-do 443-742 Korea School of Mechanical Engineering Yeungnam University Gyeongsan Gyeongbuk 38541 Korea

There are various applied electro-optical devices, which utilize light emitting didoe(LED) chip array for applications to displays and opto-electronic sensors. In those devices, it is the one of the critical technical issues to minimize uncertain fluctuations including optical power and optical density. Due to variation in operating environment of a device, those are not corrected precisely by controlling parameters based on simple relation between parameters and resultant abovementioned ***, there is essential need to correct outputs in real-time based on correction function generated from the consideration on various operation condition. In this article, we introduce an output correction method through reporting real-time image noise reduction in the application to electro-photography with LED print head. In the technology of LED print head, as differences in optical characteristics between each LED cause vertical image noise, it should be corrected in order to obtain images that are comparable or better in quality compared to those produced by the conventional laser scanning method. Even though it seems that the method used to obtain uniform light power from each LED can solve this problem, it does not work well for high-resolution printing. Therefore, a scan method involving correction by a printed and scanned pattern is introduced through this work. The scan method is composed of correction patterns to minimize printing noise by its shape, the correction algorithm to calculate the optimized value and the printing algorithm to control gray levels in real-time precisely. We believe that the developed correction method upgrades the printing quality of the LPH printer better than commercial printers. The developed correction method can also be applied to various application areas that use an array-type light source such as display systems and lighting systems.

关键词： real-time image correction LED print head(LPH) vertical image noise electro-photography temporal correction spatial correction

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Effect of friction on the contact stress of a coated polymer gear

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Friction 2020年第6期8卷 1169-1177页

作者： Su-Min BAE Kuk-Jin SEO dae-Eun kim Department of Mechanical Engineering Yonsei UniversitySeoul 03722Republic of Korea

Polymer gears are used extensively in various ***,durability issues have been emerging because of friction at gear tooth contact *** extend the lifetime of polymer gears,a low-frictional coating has been considered as a possible *** this study,a finite element simulation method was performed to investigate the contact stress between a pair of coated polymer *** simulation included various friction coefficients(COFs)for studying the effects of friction during the *** results revealed that the friction causes the contact stress to shift over the roll angle,which is attributed to the direction of the sliding friction based on a free-body *** also investigated the effects of coating and found that a thin coating has little effect on the bulk deformation behavior of the ***,the stress distribution in the coating at the pitch point was investigated as the COF *** zero friction,three notable stress regions were observed:1)the center of the surface,2)the end of the contact,and 3)the overall contact *** COF was increased in the micro-slip region of the contact interface,both tensile and compressive stresses in the coating *** study provides significant aid to engineers for understanding the stress response of the coating applied to polymer gears to achieve an optimal design.

关键词： coating contact stress finite element method(FEM) friction polymer gear

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Material Characterization of Ni Base Alloy for Very High Temperature Reactor

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Journal of Materials Science & Technology 2013年第12期29卷 1184-1190页

作者： Dong-Jin kim Gyeong-Geun Lee dae Jong kim Su Jin Jeong Nuclear Materials Division Korea Atomic Energy Research Institute

The generation of highly efficient electricity and the production of massive hydrogen are possible using a very high temperature reactor （VHTR） among generation IV nuclear power plants. The structural material for an intermediate heat exchanger （IHX） among numerous components should be endurable at high temperature of up to 950 °C during long-term operation. Impurities inevitably introduced in helium as a coolant facilitate the material degradation by corrosion at high temperature. In the present work, the surface reactions available under controlled impure helium at 950 °C were investigated based on the thermodynamics and the corrosion tests were performed in a temperature range of 850-950 °C during 10-250 h for commercial Alloy 617 as a candidate material for an IHX. Moreover, the mechanical property and microstructure for nickel-based alloys fabricated in laboratory were evaluated as a function of the processing parameters such as hot rolling and heat treatment conditions. From the reaction rate constant obtained from an impure helium control system for a material evaluation, it was predicted that the outer oxide layer thickness, internal oxide depth, and carbide- depleted zone depth reach about 116, 600 and 1000 μm, respectively when Alloy 617 is exposed to an impure helium environment at 950 ~C for 20 years. For Ni-Cr-Co-Mo alloy, subsequent annealing and a combination of cold working and subsequent annealing following solution annealing caused increases in the grain boundary carbide coverage and size. The angular distribution of the grain boundary as well as the carbide distribution was also changed leading to a consequent improvement of the mechanical property at 950 °C in air.

关键词： Nickel base alloy Intermediate heat exchanger High temperature reactor Corrosion Mechanical property

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Evaluation of the performance of a soft X-ray charger for the bipolar charging of nanoparticles

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Particuology 2015年第1期13卷 165-169页

作者： Young Hun Yoon Choonkeun Bong dae Seong kim Department of Integrated Environmental Systems Pyeongtaek University GreenSolus Co. Global Frontier Center for Multiscale Energy Systems Seoul National University

The use of soft X-rays in a neutralizer represents an alternative technique that could replace conventional radioactive sources. In this study, we evaluated the charging characteristics of a soft X-ray aerosol neu- tralizer. In addition, the results from the evaluation of the soft X-ray charger were compared with results obtained using a neutralizer incorporating an 241 Am radioactive source. The tandem differential mobility analyzer technique was used previously to determine the size-dependent positive, negative, and neutral charge fractions of a soft X-ray neutralizer. This technique was used to show that the neutral fractions obtained using the soft X-ray charger agreed well with the predictions of bipolar diffusion charging the- ory, and that the soft X-ray charger could be used as a neutralizer for a scanning mobility particle sizer system.

关键词： Soft X-ray Neutralizer Bipolar charger Nanoparticle TDMA

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Influence of CaO on damping capacity and mechanical properties of Mg alloy

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中国有色金属学会会刊：英文版 2009年第B9期19卷 76-79页

作者： Dong-In JANG Jin-Kyu LEE dae-Up kim Shae-K kim Advanced Material Division Korea Institute of Industrial Technology Hyudai Mobis

For developing cost effective damping Mg alloys with high damping capacity and better mechanical properties, the microstructures, the mechanical properties at room temperature and the damping capacity of Mg alloy adding CaO were investigated and compared with those of K1A alloy. CaO adding into pure Mg maintains the damping capacity and increases the ultimate tensile strength compared with those of pure Mg. Mg-CaO alloy can be regarded as cost-effective damping alloy with high damping and mechanical properties as well as with the advantages of improving oxidation and burning resistances.

关键词：阻尼能力力学性能镁合金氧化钙成本效益微观结构阻尼性能电阻合金

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Optimization of post-warranty sequential inspection for second-hand products

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Journal of Systems Engineering and Electronics 2017年第4期28卷 793-800页

作者： dae-Kyung kim Jae-Hak Lim Dong Ho Park Department of Statistics Chonbuk National University Department of Management & Accounting Hanbat National University Industry Academic Cooperation Foundation Hallym University

This paper considers an optimal sequential inspection schedule for a second-hand product after that the free nonrenewable warranty is expired. The length of warranty is prespecified and during the warranty period, the product is minimally repaired by the dealer when it fails. Following the expiration of the non-renewing warranty, the product is inspected and upgraded sequentially a fixed number of times at the expenses of the *** each inspection, the failure rate of the product is reduced proportionally so that the product is upgraded. The product is assumed to deteriorate as it ages and the replacement of the product occurs when a fixed number of inspections are rendered. In addition,the intervals between two successive inspections are assumed to decrease monotonically. The main objective of this paper is to determine the optimal improvement level to upgrade the product at each inspection so that the expected maintenance cost during the life cycle of the product is minimized from the perspective of the customer. Under the given cost structures, we derive an explicit formula to obtain the expected maintenance cost incurred during the life cycle of the product and discuss the method to find the optimal level of the improvement analytically in case the failure times follow the Weibull distribution. Numerical results are analyzed to observe the impact of relevant parameters on the optimal solution.

关键词： second-hand product sequential inspection upgrade action life cycle of the product expected maintenance cost free non-renewable warranty

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Development of polyimide films reinforced with boron nitride and boron nitride nanosheets for transparent flexible device applications

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Nano Research 2018年第5期11卷 2366-2378页

作者： You Jin Min Kyeong-Hee Kang dae-Eun kim Department of Mechanical Engineering Yonsei University 50 Yonsei-ro Seodaemun-gu Seoul 03722 Republic of Korea

The benefits of reinforcing polyimide （PI） films with boron nitride （BN） particles and boron nitride nanosheets （BNNSs） were assessed with the aim of enhancing their thermal, optical, and mechanical properties for flexible device applications. BNNSs were prepared from BN particles using a liquid-phase exfoliation method assisted by an ultrasonic probe-type sonicator and centrifugator. PI-based composite films blended with BNNSs and BN particles were fabricated at various concentrations via mechanical stirring and spin coating. The transparency of the PI/BNNS composite films remained almost the same as that of pure PI films up to 3 wt.% whereas the transparency of the PI/BN composite films decreased with increasing concentration of the BN fillers at 550 nm. The thermal stability improved significantly with increasing concentrations of both BN and BNNS relative to that of pure PI films. The temperature for 5% weight loss of the PI/BNNS composite film was higher than that of the PI/BN composite film at the same filler concentration. The composite films with 2 wt.% BN or BNNS showed the lowest wear rate, and the PI/BNNS composite films showed more stable frictional behavior compared to the PI/BN composite films. In addition, bending tests showed that the PI/BNNS composite films exhibited excellent flexibility compared to the PI/BN composite films. Overall, the results indicate that the BNNS can be effectively used as a filler that can enhance the thermal and mechanical properties of polymer materials for flexible device applications.

关键词： polyimide (PI) boron nitride (BN) transparency thermal properties flexibility tribology

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Study of Degenerate Poly-Bernoulli Polynomials byλ-Umbral Calculus

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Computer Modeling in Engineering & Sciences 2021年第10期129卷 393-408页

作者： Lee-Chae Jang dae San kim Hanyoung kim Taekyun kim Hyunseok Lee Graduate School of Education Konkuk UniversitySeoul143-701Korea Department of Mathematics Sogang UniversitySeoul121-742Korea Department of Mathematics Kwangwoon UniversitySeoul139-701Korea

Recently,degenerate poly-Bernoulli polynomials are defined in terms of degenerate polyexponential functions by *** aim of this paper is to further examine some properties of the degenerate poly-Bernoulli polynomials by using three formulas from the recently developed‘λ-umbral calculus.’In more detail,we represent the degenerate poly-Bernoulli polynomials by Carlitz Bernoulli polynomials and degenerate Stirling numbers of the first kind,by fully degenerate Bell polynomials and degenerate Stirling numbers of the first kind,and by higherorder degenerate Bernoulli polynomials and degenerate Stirling numbers of the second kind.

关键词： Degenerate poly-Bernoulli polynomials degenerate polyexponential functions λ-umbral calculus

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Parasitic Robot System for Waypoint Navigation of Turtle

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Journal of Bionic Engineering 2017年第2期14卷 327-335页

作者： dae-Gun kim Serin Lee Cheol-Hu kim Sungho Jo Phill-Seung Lee Department of Mechanical Engineering Korea Advanced Institute of Science and Technology (KAIST) 373-1 Guseong-dong Yuseong-gu Daejeon 34141 Republic of Korea Institute for Infocomm Research 1 Fusionopolis Way #21-01 Connexis Singapore Department of Computer Science Korea Advanced Institute of Science and Technology (KAIST) 373-1 Guseong-dong Yuseong-gu Daejeon 34141 Republic of Korea

In research on small mobile robots and biomimetic robots, locomotion ability remains a major issue despite many advances in technology. However, evolution has led to there being many real animals capable of exceUent locomotion. This paper presents a ＂parasitic robot system＂ whereby locomotion abilities of an animal are applied to a robot task. We chose a turtle as our first host animal and designed a parasitic robot that can perform ＂operant conditioning＂. The parasitic robot, which is attached to the turtle, can induce object-tracking behavior of the turtle toward a Light Emitting Diode （LED） and positively reinforce the behavior through repeated stimulus-response interaction. After training sessions over five weeks, the robot could successfully control the direction of movement of the trained turtles in the waypoint navigation task. This hybrid animal-robot interaction system could provide an alternative solution to some of the limitations of conventional mobile robot systems in various fields, and could also act as a useful interaction system for the behavioral sciences.

关键词： parasitic robot operant conditioning waypoint navigation red-eared slider trachemys scripta elegans

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Materials and devices for flexible and stretchable photodetectors and light-emitting diodes

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Nano Research 2021年第9期14卷 2919-2937页

作者： Jun-Kyul Song Min Sung kim Seungwon Yoo Ja Hoon Koo dae-Hyeong kim Center for Nanoparticle Research Institute for Basic Science(IBS)Seoul 08826Republic of Korea School of Chemical and Biological Engineering and Institute of Chemical Processes Seoul National UniversitySeoul 08826Republic of Korea Interdisciplinary Program for Bioengineering Seoul National UniversitySeoul 08826Republic of Korea Department of Materials Science and Engineering Seoul National UniversitySeoul 08826Republic of Korea

Recently,significant efforts have been directed at overcoming the limitations of conventional rigid optoelectronic devices,particularly their poor mechanical stability under bending,folding,and stretching *** of major approaches for rendering optoelectronic devices mechanically deformable is to replace the conventional electronic/optoelectronic materials with functional nanomaterials or organic materials that are intrinsically flexible/***,advanced device designs and unconventional fabrication methods have also contributed to the development of soft optoelectronic ***,new devices such as bio-inspired curved image sensors,wearable light emitting devices,and deformable bio-integrated optoelectronic devices have been *** this review,recent progress in the development of soft optoelectronic materials and devices is ***,various materials such as nanomaterials,organic materials,and their hybrids that are suitable for developing deformable photodetectors,are ***,the nanomaterials and organic/polymeric materials that are applicable in deformable light-emitting diodes are ***,representative system-level applications of flexible and stretchable photodetectors and light-emitting diodes are reviewed,and future prospects are discussed.

关键词： nanomaterial organic material photodetector light-emitting diode flexible optoelectronics stretchable optoelectronics

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