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Measuring nanoscale friction at graphene step edges

Friction 2020年第4期8卷 802-811页

作者： Zhe ChEN seong h.kim Department of Chemical Engineering and Materials Research Institute Pennsylvania State UniversityUniversity ParkPA 16802USA

Although graphene is well known for super-lubricity on its basal plane, friction at its step edge is not well understood and contradictory friction behaviors have been reported. In this study, friction of mono-layer thick graphene step edges was studied using atomic force microscopy (AFM) with a Si tip in dry nitrogen atmosphere. It is found that, when the tip slides over a'buried' graphene step edge, there is a resistive force during the step-up motion and an assistive force during the step-down motion due to the topographic height change. The magnitude of these two forces is small and the same in both step-up and step-down motions. As for the'exposed' graphene step edge, friction increases in magnitude and exhibits more complicated behaviors. During the step-down motion of the tip over the exposed step edge, both resistive and assistive components can be detected in the lateral force signal of AFM if the scan resolution is sufficiently high. The resistive component is attributed to chemical interactions between the functional groups at the tip and step-edge surfaces, and the assistive component is due to the topographic effect, same as the case of buried step edge. If a blunt tip is used, the distinct effects of these two components become more prominent. In the step-up scan direction, the blunt tip appears to have two separate topographic effects–elastic deformation of the contact region at the bottom of the tip due to the substrate height change at the step edge and tilting of the tip while the vertical position of the cantilever (the end of the tip) ascends from the lower terrace to the upper terrace. The high-resolution measurement of friction behaviors at graphene step edges will further enrich understanding of interfacial friction behaviors on graphene-covered surfaces.

关键词： friction graphene step edge atomic force microscopy tip bluntness

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Vapors in the ambient-A complication in tribological studies or an engineering solution of tribological problems?

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Friction 2015年第2期3卷 85-114页

作者： Ala ALAZIZI Anthony J.BARThEL Nicholas D.SURDYKA Jiawei LUO seong h.kim Department of Chemical Engineering and Materials Research Institute Pennsylvania State UniversityUniversity ParkPA 16802USA

Tribology involves not only two-body contacts of two solid materials-a substrate and a counter-surface;it often involves three-body contacts whether the third body is intentionally introduced or inevitably added during the sliding or *** intentionally added third body could be lubricant oil or engineered nano-material used to mitigate the friction and wear of the sliding *** inevitably added third body could be wear debris created from the substrate or the counter surface during *** in the absence of any solid third-body between the sliding surfaces,molecular adsorption of water or organic vapors from the surrounding environment can dramatically alter the friction and wear behavior of solid surfaces tested in the absence of lubricant *** review article covers the last case:the effects of molecular adsorption on sliding solid surfaces both inevitably occurring due to the ambient test and intentionally introduced as a solution for engineering *** will review how adsorbed molecules can change the course of wear and friction,as well as the mechanical and chemical behavior,of a wide range of materials under sliding conditions.

关键词： vapor phase lubrication environmental effect

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Dragonfly Interaction Algorithm for Optimization of Queuing Delay in Industrial Wireless Networks

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Journal of Bionic Engineering 2024年第1期21卷 447-485页

作者： Sanjay Bhardwaj Da-hye kim Dong-seong kim Department of IT Convergence Engineering ICT Convergence Research CenterKumoh National Institute of TechnologyGumiSouth Korea

In industrial wireless networks,data transmitted from source to destination are highly *** often leads to the queuing of the data,and poor management of the queued data results in excessive delays,increased energy consumption,and packet ***,a nature-inspired-based Dragonfly Interaction Optimization Algorithm(DMOA)is proposed for optimization of the queue delay in industrial wireless *** term“interaction”herein used is the characterization of the“flying movement”of the dragonfly towards damselflies(female dragonflies)for *** a result,interaction is represented as the flow of transmitted data packets,or traffic,from the source to the base *** includes each and every feature of dragonfly movement as well as awareness of the rival dragonflies,predators,and damselflies for the desired optimization of the queue *** features are juxtaposed as noise and interference,which are further used in the calculation of industrial wireless metrics:latency,error rate(reliability),throughput,energy efficiency,and fairness for the optimization of the queue *** analysis,convergence analysis,the Wilcoxon test,the Friedman test,and the classical as well as the 2014 IEEE Congress of Evolutionary Computation(CEC)on the benchmark functions are also used for the evaluation of DMOA in terms of its robustness and *** results demonstrate the robustness of the proposed algorithm for both classical and benchmarking functions of the IEEE CEC ***,the accuracy and efficacy of DMOA were demonstrated by means of the convergence rate,Wilcoxon testing,and ***,fairness using Jain’s index in queue delay optimization in terms of throughput and latency,along with computational complexity,is also evaluated and compared with other *** results show that DMOA exceeds other bio-inspired optimization algorithms in terms of fairness in queue delay management and average packet *** proposed a

关键词： Dragonfly Damselfly Interaction Queuing delay Optimization Industrial wireless networks

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Tracking of horizontal alignment of the long and large diameter uncharged hole in NATM tunnel

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Underground Space 2024年第3期16卷 18-28页

作者： Min-seong kim Sean Seungwon Lee Department of Energy and Resources Engineering Chonnam National UniversityGwangju 61186Republic of Korea Department of Earth Resources and Environmental Engineering Hanyang UniversitySeoul 04763Republic of Korea

The long and large diameter uncharged hole boring(LLB)method is a cut blasting method that minimizes blast-induced vibrations by creating long and large diameter uncharged holes at the excavation face of tunnels prior to tunnel *** in this method typically uses a 50 m long with a 382 mm diameter hammer bit in the horizontal direction at the tunnel ***,the significant weight and uni-directional rotation of the rod head,as well as variables such as geological characteristics,machine conditions,and inexperienced operators result in significant deviation from the target borehole alignment that hinders the vibration-dampening effect of the uncharged ***,since there is no method to verify the alignment of the boreholes until main tunnel construction,borehole misalignment is often not discovered until weeks after construction,which requires tunnel construction to cease until the equipment can be remobilized and an additional borehole be created,causing significant delays and increased costs for the entire tunnel *** this study,the borehole alignment tracking and ground exploration system(BGS)is developed to predict and monitor the quality and alignment of boreholes for cut blasting methods such as the LLB methods immediately after *** BGS was subsequently tested at a subway construction site to evaluate its performance in the *** measurements yielded by the BGS were compared with manually measured boring positions at every 5 m along the *** the BGS showed a maximum deviation of approximately 12%at a local point where the hole surface was relatively rough,the accuracy for the final boring position was approximately 97%,demonstrating excellent precision of the alignment tracking *** BGS demonstrates excellent performance in predicting ground conditions and the boring quality of a cut hole immediately after drilling,and shows promise in various other applications for monitoring borehole alignment.

关键词： Tunnel blasting LLB method Drilling deviation Vertical sagging horizontal alignment tracking BGS

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Incorporation of Ionic Conductive Polymers into Sulfide Electrolyte-Based Solid-State Batteries to Enhance Electrochemical Stability and Cycle Life

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Energy & Environmental Materials 2024年第6期7卷 4-12页

作者： Juhyoung kim Woonghee Choi seong-Ju hwang Dong Wook kim Advanced Materials Division Korea Research Institute of Chemical Technology(KRICT)Daejeon 34114Korea Department of Material Science and Engineering Yonsei UniversitySeoul 03722Korea Department of Material Science and Engineering Seoul National UniversitySeoul 08826Korea Advanced Materials and Chemical Engineering University of Science and Technology(UST)Daejeon 34113Korea

Sulfide-based inorganic solid electrolytes are promising materials for high-performance safe solid-state *** high ion conductivity,mechanical characteristics,and good processability of sulfide-based inorganic solid electrolytes are desirable properties for realizing high-performance safe solid-state batteries by replacing conventional liquid ***,the low chemical and electrochemical stability of sulfide-based inorganic solid electrolytes hinder the commercialization of sulfide-based safe solid-state ***,the instability of sulfide-based inorganic solid electrolytes is intensified in the cathode,comprising various *** this study,carbonate-based ionic conductive polymers are introduced to the cathode to protect cathode materials and suppress the reactivity of sulfide *** instruments,including electrochemical spectroscopy,X-ray photoelectron spectroscopy,and scanning electron microscopy,confirm the chemical and electrochemical stability of the polymer electrolytes in contact with sulfide-based inorganic solid ***-based solid-state cells show stable electrochemical performance over 100 cycles when the ionic conductive polymers were applied to the cathode.

关键词： composite cathode electrochemical stability ionic conductive polymer solid-state battery sulfide solid electrolyte

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Liquid crystal-integrated metasurfaces for an active photonic platform

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Opto-Electronic Advances 2024年第6期7卷 5-29页

作者： Dohyun Kang hyeonsu heo Younghwan Yang Junhwa seong hongyoon kim Joohoon kim Junsuk Rho Department of Mechanical Engineering Pohang University of Science and Technology(POSTECH)Pohang 37673Republic of Korea Department of Chemical Engineering Pohang University of Science and Technology(POSTECH)Pohang 37673Republic of Korea Department of Electrical Engineering Pohang University of Science and Technology(POSTECH)Pohang 36763Republic of Korea POSCOPOSTECh-RIST Convergence Research Center for Flat Optics and Metaphotonics Pohang 37673Republic of Korea National Institute of Nanomaterials Technology(NINT) Pohang 37673Republic of Korea

Metasurfaces have opened the door to next-generation optical devices due to their ability to dramatically modulate electromagnetic waves at will using periodically arranged ***,metasurfaces typically have static optical responses with fixed geometries of nanostructures,which poses challenges for implementing transition to technology by replacing conventional optical *** solve this problem,liquid crystals(LCs)have been actively employed for designing tunable metasurfaces using their adjustable birefringent in real ***,we review recent studies on LCpowered tunable metasurfaces,which are categorized as wavefront tuning and spectral *** to numerous reviews on tunable metasurfaces,this review intensively explores recent development of LC-integrated *** the end of this review,we briefly introduce the latest research trends on LC-powered metasurfaces and suggest further directions for improving *** hope that this review will accelerate the development of new and innovative LC-powered devices.

关键词： tunable metasurface liquid crystal active metasurface electrically tunable optical system

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Organic X-Ray Image Sensors Using a Medium Bandgap Polymer Donor with Low Dark Current

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Energy & Environmental Materials 2024年第6期7卷 230-237页

作者： Jong-Woon ha Seung hun Eom Bo Kyung Cha Seyeong Song hyeong Ju Eun Jong h.kim Jong Mok Park BongSoo kim Byoungwook Park Seo-Jin Ko Sung Cheol Yoon Changjin Lee In hwan Jung Do-hoon hwang Department of Chemistry Chemistry Institute for Functional MaterialsPusan National UniversityBusan 46241Korea Division of Advanced Energy Materials Research Center Korea Research Institute of Chemical Technology(KRICT)Daejeon 34114Korea Electro-Medical Device Research Center Korea Electrotechnology Research Institute(KERI)Ansan 15588Korea Graduate School of Carbon Neutrality School of Energy and Chemical EngineeringUlsan National Institute of Science and Technology(UNIST)Ulsan 44919Korea Department of Molecular Science and Technology Ajou UniversitySuwon 16449Korea Research Center for Advanced Specialty Chemicals Korea Research Institute of Chemical TechnologyUlsan 44412Korea Department of Chemistry Ulsan National Institute of Science and Technology(UNIST)Ulsan 44919Korea Department of Organic and Nano Engineering Human-Tech Convergence ProgramHanyang University222 Wangsimni-roSeongdong-guSeoul 04763Korea

The development of portable X-ray detectors is necessary for diagnosing fractures in unconscious patients in emergency ***,this is quite challenging because of the heavy weight of the scintillator and silicon *** weight and thickness of X-ray detectors can be reduced by replacing the silicon layer with an organic *** study presents a novel bithienopyrroledione-based polymer donor that exhibits excellent photodetection properties even in a thick photoactive layer(~700 nm),owing to the symmetric backbone and highly soluble molecular structure of *** ability of bithienopyrroledione-based polymer donor to strongly suppress the dark current density(Jd~10−10 A cm^(−2))at a negative bias(−2.0 V)while maintaining high responsivity(R=0.29 A W−1)even at a thickness of 700 nm results in a maximum shot-noise-limited specific detectivity of D_(sh)^(*)=2.18×10^(13)Jones in the organic *** organic photodetectors are developed by slot-die coating for use in X-ray detectors,which exhibit D_(sh)^(*)=2.73×10^(12)Jones with clear rising(0.26 s)and falling(0.29 s)response times upon X-ray *** reliability is also proven by linear response of the X-ray detector,and the X-ray detection limit is 3 mA.

关键词： low dark current low detection limit organic photodetector printable X-ray

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Tailoring Classical Conditioning Behavior in TiO_(2) Nanowires:ZnO QDs-Based Optoelectronic Memristors for Neuromorphic hardware

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Nano-Micro Letters 2024年第7期16卷 265-280页

作者： Wenxiao Wang Yaqi Wang Feifei Yin hongsen Niu Young-Kee Shin Yang Li Eun-seong kim Nam-Young kim School of Information Science and Engineering University of JinanJinan 250022People’s Republic of China RFIC Centre NDAC CentreKwangwoon UniversityNowon-guSeoul 139-701South Korea Department of Electronics Engineering Kwangwoon UniversityNowon-GuSeoul 139-701South Korea School of Microelectronics Shandong UniversityJinan 250101People’s Republic of China Department of Molecular Medicine and Biopharmaceutical Sciences Seoul National UniversitySeoul 08826South Korea

Neuromorphic hardware equipped with associative learn-ing capabilities presents fascinating applications in the next generation of artificial ***,research into synaptic devices exhibiting complex associative learning behaviors is still ***,an optoelec-tronic memristor based on Ag/TiO_(2) Nanowires:ZnO Quantum dots/FTO was proposed and constructed to emulate the biological associative learning *** implementation of synaptic behaviors,including long and short-term plasticity,and learning-forgetting-relearning behaviors,were achieved in the device through the application of light and electrical *** the optoelectronic co-modulated characteristics,a simulation of neuromorphic computing was conducted,resulting in a handwriting digit recognition accuracy of 88.9%.Furthermore,a 3×7 memristor array was constructed,confirming its application in artificial visual *** importantly,complex biological associative learning behaviors were emulated by mapping the light and electrical stimuli into conditioned and unconditioned stimuli,*** training through associative pairs,reflexes could be triggered solely using light ***-sively,under specific optoelectronic signal applications,the four features of classical conditioning,namely acquisition,extinction,recovery,and generalization,were elegantly *** work provides an optoelectronic memristor with associative behavior capabilities,offering a pathway for advancing brain-machine interfaces,autonomous robots,and machine self-learning in the future.

关键词： Artificial intelligence Classical conditioning Neuromorphic computing Artificial visual memory Optoelectronic memristors ZnO Quantum dots

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Vastly Synergistic Fe_(2)CuNiS_(4)-Nanoarchitectures Anchored 2D-Nano-Sandwich Derived from Flower-Like-CuFeS_(2)/N-Graphene and Cube-Like-NiFeS_(2)/N-CNTs for Water Oxidation and Nitrophenol Reduction

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Energy & Environmental Materials 2024年第6期7卷 274-289页

作者： Gopiraman Mayakrishnan Ramkumar Vanaraj Junpeng Xiong Muhammad Farooq Azeem Ullah Keqin Zhang seong Cheol kim Ick Soo kim Nano Fusion Technology Research Group Division of Molecules and PolymersInstitute for Fiber Engineering(IFES)Interdisciplinary Cluster for Cutting Edge Research(ICCER)Shinshu UniversityTokida 3-15-1UedaNagano 386-8567Japan School of Chemical Engineering Yeungnam UniversityGyeongsan 38541Korea Graduate School of Medicine Scienceand TechnologyShinshu UniversityTokida 3-15-1UedaNagano 386-8567Japan National Engineering Laboratory for Modern Silk College of Textile and Clothing EngineeringSoochow UniversitySuzhou 215123China

Surface area,pore properties,synergistic behavior,homogenous dispersion,and interactions between carbon matrix and metal-nanostructures are the key factors for achieving the better performance of carbon-metal based(electro)***,the traditional hydro-or solvothermal preparation of(electro)catalysts,particularly,bi-or tri-metallic nanostructures anchored graphene(G)or carbon nanotubes(CNTs),often pose to poor metal–support interaction,low synergism,and patchy *** first,bimetallic flower-like-CuFeS_(2)/NG and cube-like-NiFeS_(2)/NCNTs nanocomposites were prepared by solvothermal *** resultant bimetallic nanocomposites were employed to derive the 2D-nano-sandwiched Fe_(2)CuNiS_(4)/NGCNTs-SW(electro)catalyst by a very simple and green urea-mediated“mix-heat”*** desired physicochemical properties of Fe_(2)CuNiS_(4)/NGCNTs-SW such as multiple active sites,strong metal-support interaction,homogenous dispersion and enhanced surface area were confirmed by various microscopic and spectroscopic *** the best of our knowledge,this is the first urea-mediated“mix-heat”method for preparing 2D-nano-sandwiched carbon-metal-based(electro)*** Fe_(2)CuNiS_(4)/NGCNTs-SW was found to be highly effective for alkaline-mediated oxygen evolution reaction at low onset potential of 284.24 mV,and the stable current density of 10 mA cm^(−2) in 1.0 m KOh for 10 ***,the Fe_(2)CuNiS_(4)/NGCNTs-SW demonstrated excellent catalytic activity in the reduction of 4-nitrophenol with good kapp value of 87.71×10^(−2)s^(-1)and excellent reusability over five ***,the developed urea-mediated“mix-heat”method is highly efficient for the preparation of metal-nanoarchitectures anchored 2D-nano-sandwiched(electro)catalysts with high synergism,uniform dispersion and excellent metal-support interaction.

关键词： (electro)catalyst metal-sulfide nanoarchitectures mix-heat N-graphene/NCNTs synergistic effect urea

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Random pinhole attenuator for high-power laser beams

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high Power Laser Science and Engineering 2024年第3期12卷 116-121页

作者： seong Cheol Park hyeok Yun Jin Woo Yoon seong Ku Lee Jae hee Sung Il Woo Choi Chang hee Nam Kyung Taec kim Department of Physics and Photon Science Gwangju Institute of Science and TechnologyGwangjuRepublic of Korea Center for Relativistic Laser Science Institute for Basic ScienceGwangjuRepublic of Korea Advanced Photonics Research Institute Gwangju Institute of Science and TechnologyGwangjuRepublic of Korea

The intensity attenuation of a high-power laser is a frequent task in the measurements of optical *** intensity can be attenuated by inserting an optical element,such as a partial reflector,polarizer or absorption *** devices are,however,not always easily applicable,especially in the case of ultra-high-power lasers,because they can alter the characteristics of a laser beam or become easily *** this study,we demonstrated that the intensity of a laser beam could be effectively attenuated using a random pinhole attenuator(RPA),a device with randomly distributed pinholes,without changing the beam *** this device,a multi-PW laser beam was successfully attenuated and the focused beam profile was measured without any alterations of its *** addition,it was confirmed that the temporal profile of a laser pulse,including the spectral phase,was ***,the RPA possesses significant potential for a wide range of applications.

关键词： high-power laser intensity attenuation laser diagnostics

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