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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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Physical properties of sprayed antimony doped tin oxide thin films:The role of thickness

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Journal of Semiconductors 2011年第5期32卷 10-17页

作者： A.R.Babar S.S.Shinde A.V.Moholkar C.h.Bhosale J.h.kim K.y.Rajpure Electrochemical Materials Laboratory Department of PhysicsShivaji UniversityKolhapur-416 004India Department of Materials Science and Engineering Chonnam National University300 Yongbong-DongBuk-GuGwangju500-757South Korea

Transparent conducting antimony doped tin oxide （Sb：SnO2） thin films have been deposited onto pre- heated glass substrates using a spray pyrolysis technique by varying the quantity of spraying solution. The structural, morphological, X-ray photoelectron spectroscopy, optical, photoluminescence and electrical properties of these films have been studied. It is found that the films are polycrystalline in nature with a tetragonal crystal structure having orientation along the （211） and （112） planes. Polyhedrons like grains appear in the FE-SEM images. The average grain size increases with increasing spraying quantity. The compositional analysis and electronic behaviour of Sb：SnO2 thin films were studied using X-ray photoelectron spectroscopy. The binding energy of Sn3ds/2 for all samples shows the Sn^4＋ bonding state from SnO2. An intensive violet luminescence peak near 395 nm is observed at room temperature due to oxygen vacancies or donor levels formed by Sb^5＋ ions. The film deposited with 20 cc solution shows 70 % transmittance at 550 nm leading to the highest figure of merit （2.11 × 10^-3 Ω^-1）. The resistivity and carrier concentration vary over 1.22 × 10^-3 to 0.89 × 10^-3Ω cm and 5.19 ×10^20 to 8.52 × 10^20 cm^-3, respectively.

关键词： semiconductors microstructure optical properties electrical properties

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Complex regulatory effects of gut microbial short-chain fatty acids on immune tolerance and autoimmunity

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Cellular & Molecular Immunology 2023年第4期20卷 341-350页

作者： Chang h.kim Department of Pathology University of Michigan School of MedicineAnn ArborMI48109USA Mary h.Weiser Food Allergy Center Center for Gastrointestinal Researchand Rogel Center for Can

Immune tolerance deletes or suppresses autoreactive lymphocytes and is established at multiple levels during the development,activation and effector phases of T and B *** mechanisms are cell-intrinsically programmed and critical in preventing autoimmune *** have witnessed the existence of another type of immune tolerance mechanism that is shaped by lifestyle choices,such as diet,microbiome and microbial ***-chain fatty acids(SCFAs)are the most abundant microbial metabolites in the colonic lumen and are mainly produced by the microbial fermentation of prebiotics,such as dietary *** review focuses on the preventive and immunomodulatory effects of SCFAs on *** tissue-and disease-specific effects of dietary fiber,SCFAs and SCFA-producing microbes on major types of autoimmune diseases,including type I diabetes,multiple sclerosis,rheumatoid arthritis and lupus,are ***,their key regulatory mechanisms for lymphocyte development,tissue barrier function,host metabolism,immunity,autoantibody production,and inflammatory effector and regulatory lymphocytes are *** shared and differential effects of SCFAs on different types and stages of autoimmune diseases are discussed.

关键词： Short-chain fatty acids Immune tolerance Diabetes mellitus Rheumatoid arthritis Lupus Multiple sclerosis

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Control of lymphocyte functions by gut microbiota-derived short-chain fatty acids

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Cellular & Molecular Immunology 2021年第5期18卷 1161-1171页

作者： Chang h.kim Department of Pathology and Mary h.Weiser Food Allergy Center University of Michigan School of MedicineAnn ArborMIUSA

A mounting body of evidence indicates that dietary fiber(DF)metabolites produced by commensal bacteria play essential roles in balancing the immune ***,considered nonessential nutrients in the past,is now considered to be necessary to maintain adequate levels of immunity and suppress inflammatory and allergic ***-chain fatty acids(SCFAs),such as acetate,propionate,and butyrate,are the major DF metabolites and mostly produced by specialized commensal bacteria that are capable of breaking down DF into simpler saccharides and further metabolizing the saccharides into *** act on many cell types to regulate a number of important biological processes,including host metabolism,intestinal functions,and immunity *** review specifically highlights the regulatory functions of DF and SCFAs in the immune system with a focus on major innate and adaptive *** information regarding how SCFAs regulate innate lymphoid cells,T helper cells,cytotoxic T cells,and B cells and how these functions impact immunity,inflammation,and allergic responses are discussed.

关键词： Microbiota Dietary fiber Short-chain fatty acids Innate lymphoid cells B cells Th1 Th17 Tregs CD8 Microbial metabolites

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Numerical simulation and experimental study for rheo-forged component using direct and indirect die system

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Transactions of Nonferrous Metals Society of China 2010年第9期20卷 1799-1804页

作者： h.h.kim C.G.KANG Precision Manufacturing Systems Division Pusan National University School of Mechanical Engineering Pusan National University

Sand casting and die casting processes have been used widely for complex automotive products such as knuckle, arm, ***, a part fabricated by casting has limited strength due to manufacturing defects such as the dendrite structure, segregation and *** an attempt to offer a solution to these problems, forging has been used as an alternative ***, the forging process provides limited formability for complex shape ***-forging of metal offers not only superior mechanical strength but also requires significantly lower machine loads than solid forming *** order to produce semi-solid materials of the desired microstructure, a stirring process is applied during solidification of molten *** results of an A356 aluminum alloy sample, which are obtained by experiment and by simulation using DEFORM 3D, are present.

关键词： rheo-forging A356 alloy formability forming defects

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Time-Resolved Photoluminescence Studies of Indium-Rich InGaN Alloys

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Chinese Physics Letters 2005年第2期22卷 472-474页

作者：陈光德竹有章颜国君苑进社 K.h.kim J.y.Lin h.X.Jiang DepartmentofAppliedPhysics Xi'anJiaotongUniversityXi'an710049 DepartmentofPhysics KansasStateUniversityManhattanKansas66506-2601USA DepartmentofAppliedPhysics Xi'anJiaotongUniversityXi'an710049

Time-resolved photoluminescence (PL) spectroscopy has be used to investigateindium-rich InGaN alloys grown on sapphire substrates by metal organic chemical vapor *** measurement indicates two dominant emission lines originating from phase-separatedhigh- and low-indium-content regions. Temperature and excitation intensity dependence of the twomain emission lines in these InGaN alloys have been measured. Temperature and energy dependence ofPL decay lifetime show clearly different decay behaviour for the two main lines. Our results showthat photo-excited carriers are deeply localized in the high indium regions while photo-excitedcarriers can be transferred within the low-indium-content regions as well as to high-contentregions.

关键词： OPTICAL-PROPERTIES EMITTING-DIODES QUANTUM-WELL FILMS

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Anomalously Strong Scattering of Spontaneously Produced Laser Radiation in the First Free-Electron Laser and Study of Free-Electron Two-Quantum Stark Lasing in an Electric Wiggler with Quantum-Wiggler Electrodynamics

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Chinese Physics Letters 2006年第6期23卷 1422-1425页

作者： S. h. kim Department of Physics University of Texas at Arlington PO Box 19059 Arlington Texas 76019 USA

We calculate the scattering cross section of an electron with respect to the spontaneously produced laser radiation in the first free-electron laser （FEL） with quantum-wiggler electrodynamics （QWD）. The cross section is 1016 times the Thomson cross section, confirming the result obtained by a previous analysis of the experimental data. A QWD calculation show that spontaneous emission in an FEL using only an electric wiggler can be very strong while amplification through net stimulated emission is practically negligible.

关键词： CLASSICAL ELECTRODyNAMICS RELATIVISTIC ELECTRONS ThERMODyNAMICS EXPLANATION EMISSION

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Electric-Wiggler-Enhanced Three-Quantum Scattering and the Output Power Affected by this Scattering in a Free-Electron Laser

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Chinese Physics Letters 2009年第1期26卷 58-61页

作者： S. h. kim 6300 Roundrock Trail #4203 Piano Texas 75023 USA

We derive the cross section of scattering through the three-quantum interaction of an electron with the incident laser field, the emitted photon, and an axial electrostatic field produced by the magnetic wiggler in the magnetic wiggler acting as the sole zeroth-order perturbing classical field in the first free-electron laser （FEL）. In the derivation, we apply quantum-wiggler electrodynamics （QWD）. We find that this scattering predominates the usual two-quantum scattering. The output power of spontaneous free-electron two-quantum Stark emission driven by the above electrostatic field attenuated by the three-quantum scattering agrees within a factor of 10 with the measured power in the case of the first FEL.

关键词： field emission molybdenum dioxide enhancement factor

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Study of the Interface between Steel Insert and Aluminum Casting in EPC

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Journal of Materials Science & Technology 2008年第1期24卷 60-64页

作者： K.h.Choe K.S.Park B.h.Kang G.S.Cho K.y.kim K.W.Lee M.h.kim A.Ikenaga S.Koroyasu Advanced Material Processing Team Korea Institute of Industrial Technology IncheonKorea Department of Materials Engineering Korea University of Technology and Education ChoongnamKorea Department of Materials Science and Engineering Inha University IncheonKorea Department of Metallurgy and Materials Science Graduate School of Engineering Osaka Prefecture UniversityOsakaJapan Department of Mechanical and Precision Systems Teiko University UtsunomiyaJapan

The effective surface treatment method for steel insert composited with Al base metal by expendable pattern casting （EPC） process and the bonding interface between steel insert and Al base metal were *** was found that Zn plating on steel insert was effective on improving the bonding property between steel insert and Al base metal in EPC *** is thought to promote the formation of diffusion *** almost none content of Zn was observed in the boundary which had been plated on the steel insert.A diffusion layer consisting of Al,Si and Fe was formed at the insert/alloy interface and its hardness was higher than the steel insert as matter of course Al base *** layer turned out to be intermetallic compounds of Al-Si-Fe *** pouring temperature promoted the diffusion of Fe into Al alloy,so Fe content in intermetallic layers increased at higher pouring *** layer nearest to steel disappeared due to applied pressure.

关键词： Expendable pattern casting Insert casting Intermetallic compound Al-Si-Fesystem

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FUZZy REGRESSION MODEL TO PREDICT ThE BEAD GEOMETRy IN ThE ROBOTIC WELDING PROCESS

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Acta Metallurgica Sinica(English Letters) 2007年第6期20卷 391-397页

作者： B.S. Sung I.S. kim y. Xue h.h. kim y.h. Cha Department of Material Engineering Chosun University 375 Seosul-Dong Dong-GuGwangju 501-759 Korea Department of Mechanical Engineering Mokpo National University 61 Dorim-riChungkye-Myun Muan-Gun Jconnam 534-729 Korea Department of Mechanical Engineering Chosun University 375 Seosul-Dong Dong-GuGwangju 501-759 Korea

Recently, there has been a rapid development in computer technology, which has in turn led to develop the fully robotic welding system using artificial intelligence （AI） technology. however, the robotic welding system has not been achieved due to difficulties of the mathematical model and sensor technologies. The possibilities of the fuzzy regression method to predict the bead geometry, such as bead width, bead height, bead penetration and bead area in the robotic GMA （gas metal arc） welding process is presented. The approach, a well-known method to deal with the problems with a high degree of fuzziness, is used to build the relationship between four process variables and the four quality characteristics, respectively. Using these models, the proper prediction of the process variables for obtaining the optimal bead geometry can be determined.

关键词： robotic arc welding bead geometry fuzzy regression modelwelding quality

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