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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

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

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

FEATURE NETWORK-DRIVEN QUADRANT MAPPING FOR suMMARIZING CUSTOMER REVIEWS

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Journal of Systems Science and Systems Engineering 2017年第5期26卷 646-664页

作者： su Gon Cho Seoung Bum kim LINA KOREA Sambong-ro Jongro-gu Seoul Republic of Korea School of Industrial Management Engineering Korea University Anam-dong Seongbuk-gu Republic of Korea

With the rapid growth of e-commerce, customers increasingly write online reviews of the product they purchase. These customer reviews are one of the most valuable sources of information affecting selection of products or services. summarizing these customer reviews is becoming an interesting area of research, inspiring researchers to develop a more condensed, concise summarization for users. However, most of the current efforts at summarization are based on general product features without feature＇s relationship. As a result, these summaries either ignore feedback from customers or do a poor job of reflecting the opinions expressed in customer reviews. To remedy this summarization shortcoming, we propose a feature network-driven quadrant mapping that captures and incorporates opinions from customer reviews. Our focus is on construction of a feature network, which is based on co-occurrence and sematic similarities, and a quadrant display showing the opinions polarity of feature groups. Moreover, the proposed approach involves clustering similar product features, and thus, it is different from standard text summarization based on abstraction and extraction. The summarized results can help customers better understand the overall opinions about a product.

关键词： Customer review text summarization text mining feature network visualization

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

Fabrication of heteroatom-doped cobalt oxide yolk-shell microsphere using recycled solution from waste materials and their excellent electrochemical properties as an anode material for lithium-ion batteries

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Rare Metals 2024年第10期43卷 4934-4947页

作者： Yeong Beom kim Chanho kim Seung-Hyun kim Yun Chan Kang Dongju Lee Gi dae Park Department of Advanced Materials Engineering Chungbuk National UniversityChungbuk 28644Korea Department of Materials Science and Engineering Korea UniversitySeoul 136-713Korea Research Institute YKSintering Co.Ltd.Chungbuk 28581Korea

Heteroatom-doped transition metal oxides have attracted great attention as advanced anode materials for lithium-ion batteries due to their high theoretical capacity and superior ***,the limited resource availability has led to a substantial rise in prices for valuable metals such as Ni and Co,posing a significant challenge for their *** address this issue,recycling of these metals from waste materials have gained prominence,and particularly the recovery of Co has been mostly focused on its economic ***,we introduced a novel recycling strategy for fabrication of heteroatomdoped CoO_(x)(comprising mainly Co_(3)O_(4)with a minor CoO phase)anode with a yolk–shell structure for lithium-ion batteries,by separating Co from cemented tungsten carbide *** employing a simple leaching process and subsequent spray pyrolysis,the yolk–shell structured microsphere comprising CoO_(x)was successfully ***,the presence of other waste metals in the leachate facilitated multi-heteroatom doping during ***,the introduction of various dopants into CoO_(x)induced oxygen vacancy formation,thereby enhancing the electrochemical properties of the CoO_(x)*** a result,compared with the phase-pure(undoped)CoO_(x)yolk–shell,the heteroatom-doped CoO_(x)yolk–shell exhibited robust cycling stability(602 mAh·g^(-1)for 200 cycles at 1 A·g^(-1))and excellent rate capability(210 mAh·g^(-1)at 10 A·g^(-1)).

关键词： Recycling Heteroatom doping Cobalt oxide Anode Lithium-ion batteries

Stabilizing lithium deposition within bimodal porous SiO_(2)-TiO_(2) microspheres as 3D host structure

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Nano Research 2024年第11期17卷 10179-10188页

作者： Noeul kim Jae Hun Choi Min kim dae Soo Jung Yun Chan Kang Department of Materials Science and Engineering Korea University Anam-Dong Seongbuk-Gu Seoul 136-713 Republic of Korea Energy Storage Materials Center Korea Institute of Ceramic Engineering and Technology Soho-ro Jinju-si Gyeongnam-do 52851 Republic of Korea

Three-dimensional (3D) host materials for lithium metal anodes (LMAs) have gained attention because they can mitigate volume expansion and local current density through their large surface area and suppress the dendritic growth of lithium. Recent research on 3D host materials has focused on conductive materials;however, the benefits of 3D host materials cannot be fully utilized because lithium deposition begins at the top of the structure. Herein, we fabricate SiO_(2)-TiO_(2) composite microspheres with bimodal pore structures (bi-SiTiO) by simple spray pyrolysis. These microspheres effectively store lithium within the structure from the bottom of the electrode while preventing lithium dendrite formation. Focused ion beam-scanning transmission electron microscopy (FIB-STEM) analysis reveals that the lithiophilic properties of composite microspheres enhanced their effectiveness in storing lithium, with small pores acting as “lithium-ion sieves” for a uniform lithium-ion flux and large pores that provide sufficient volume for lithium deposition. The bi-SiTiO composite microspheres exhibit a high Coulombic efficiency of 98.5% over 200 cycles at 2.0 mA·cm^(−2) when operated in a lithium half-cell. With a high lithium loading of 5.0 mAh·cm^(−2), the symmetrical cell of the bi-SiTiO electrode sustains more than 900 h. A full cell coupled with an LiNi_(0.8)Co_(0.1)Mn_(0.1)O_(2) (NCM811) cathode also exhibits enhanced electrochemical properties in terms of cycling stability and rate capability.

关键词： lithium metal battery spray pyrolysis three-dimensional(3D)host materials bimodal pore structure lithiophilic materials

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

Development of Cloud Based Air Pollution Information System Using Visualization

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Computers, Materials & Continua 2019年第6期59卷 697-711页

作者： SangWook Han JungYeon Seo dae-Young kim SeokHoon kim HwaMin Lee Deptartment of Computer Science and Engineering Soonchungyang UniversityAsan31538Korea School of Information Technology Engineering Daegu Catholic UniversityGyeongsan38430Korea Department of Computer Software and Engineering Soonchungyang UniversityAsan31538Korea

Air pollution caused by fine dust is a big problem all over the world and fine dust has a fatal impact on human *** there are too few fine dust measuring stations and the installation cost of fine dust measuring station is very *** this paper,we propose Cloud-based air pollution information system using *** measure fine dust,we have developed an inexpensive measuring device and studied the technique to accurately measure the concentration of fine dust at the user’s *** we have developed the smartphone application to provide air pollution *** our system,we provide collected data based analytical results through effective data *** system provides information on fine dust value and action tips through the air pollution information *** it supports visualization on the map using the statistical program *** user can check the fine dust statistics map and cope with fine dust accordingly.

关键词： Air pollution visualization R big data cloud clusters