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New methods to find solutions and analy.e stability.of equilibrium of nonholonomic mechanical sy.tems

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Acta Mechanica Sinica 2018年第6期34卷 1136-1144页

作者： j.Chen y.x.guo f.x.Mei School of Aerospace Engineering Beijing Institute of TechnologyBeijing 100081China School of Phy.ics Liaoning UniversityShenyang 110000China

A large proportion of constrained mechanical sy.tems result in nonlinear ordinary.differential equations,for which it is quite difficult to find analy.ical *** initial motions method proposed by.Whittak.r is effective to deal with such problems for various constrained mechanical sy.tems,including the nonholonomic sy.tems discussed in the first part of this paper,where in addition to differential equations of motion,nonholonomic constraints *** final equations of motion for these sy.tems are obtained in the form of corresponding power ***,an alternative,direct method to determine the initial values of higher-order derivatives(q)0,(q)0,…is proposed,being different from that of *** second part of this work.analy.es the stability.of equilibrium of less complex,nonholonomic mechanical sy.tems represented by.gradient *** discuss the stability.of equilibrium of such sy.tems based on the properties of the gradient *** advantage of this novel method is its avoidance of the difficulty.of directly.establishing Ly.punov functions aimed at such unsteady.nonlinear ***,these theoretical considerations are illustrated through four examples.

关键词： Nonholonomic sy.tem Initial motions Gradient sy.tem Ly.punov function Stability

One k.nd motion of controllable constrained Birk.offian sy.tem:the absence of constraints

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Acta Mechanica Sinica 2020年第3期36卷 735-741页

作者： j.Chen f.x.Mei S.x.Liu y.x.guo School of Aerospace Engineering Beijing Institute of TechnologyBeijing 100081China School of Phy.ics Liaoning UniversityShenyang 110000China

This paper is devoted to discuss the motion of controllable constrained Birk.offian sy.tem along with its absence of *** first step is to establish the autonomous and non-autonomous differential equations of motion of the sy.tem,based on Pfaff-Birk.off ***,the existence of constraint multipliers are exhaustively.***,the definition of one k.nd motion of the sy.tem,called free motion,is given,which is described and analy.ed by.the absence of constraints that are determined by.constraint *** 2 illustrates that one sy.tem can realize its free motion by.selecting proper control *** particular,theorem 2 provides that one sy.tem can naturally.realize free motion when we consider the integral of the unconstrained Birk.offian sy.tem as the constraints of constrained Birk.offian ***,the results obtained are illustrated by.several examples.

关键词： Constrained Birk.offian sy.tem k.nematic control Absence of constraint free motion

Relationship of Corrosion Behavior Between Single-Phase Equiatomic CoCrNi,CoCrNife,CoCrNifeMn Alloy. and Their Constituents in NaCl Solution

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Acta Metallurgica Sinica(English Letters) 2021年第11期34卷 1574-1584页

作者： D.P.Wang j.W.Shen Z.Chen f.G.Chen P.y.guo y.x.Geng y.x.Wang School of Materials Science and Engineering Jiangsu University of Science and TechnologyZhenjiang 212003China

The composition is a significant issue for corrosion resistance of metallic *** reveal the correlation of corrosion behavior between multiprinciple alloy. and their constituents,a series of single-phase equiatomic alloy. of CoCrNi,CoCrNife and CoCrNifeMn was *** electrochemical and scanning electron microscope results demonstrated that corrosion resistance of the equiatomic alloy. in 0.1 M NaCl solution is located in the range but not the average value of their constituents.x-ray.photoelectron spectroscopy.analy.is indicated that the protective performance of passive film is mainly.determined by.the constituent with the highest corrosion resistance and the break.own of passive film is mainly.dominated by.the elements with the highest corrosion *** findings can guide the materials design of multiprinciple alloy. with expected corrosion performance.

关键词： High-entropy.alloy Corrosion Constituent x-ray.photoelectron spectroscopy.xPS) Passive films

Inhibition of Electromigration in Eutectic SnBi Solder Interconnect by.Plastic Prestraining

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journal of Materials Science & Technology 2011年第11期27卷 1072-1076页

作者： x.f. Zhang H.y. Liu j.D. guo j.k. Shang Sheny.ng National Laboratory.for Materials Science Institute of Metal Research Chinese Academy of Sciences Shenyang 110016 China Department of Materials Science and Engineering University of Illinois at Urbana-Champaign. Urbana. IL 61801. USA

Plastic prestraining was applied to a solder interconnect to introduce internal defects such as dislocations in order to investigate the interaction of dislocations with electromigration damage. Above a critical prestrain, Bi interfacial segregation to the anode, a clear indication of electromigration damage in SnBi solder inter- connect, was effectively.prevented. Such an inhibiting effect is apparently.contrary.to the common notion that dislocations often act as fast diffusion paths. It is suggested that the dislocations introduced by.plastic prestraining acted as sink. for vacancies in the early.stage of the electromigration process, but as the vacancies accumulated at the dislocations, climb of those dislocations prompted recovery.of the deformed samples under current stressing, greatly.decreasing the density.of dislocation and vacancy.in the solder, leading to slower diffusion of Bi atoms.

关键词： Electromigration Interfacial segregation Prestrain Dislocation Vacancy

Characterization of high-pressure die-cast hy.ereutectic Al-Si alloy. based on microstructural distribution and fracture morphology

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journal of Materials Science & Technology 2019年第6期35卷 1099-1107页

作者： x.y. jiao j. Wang C.f. Liu Z.P. guo G.D. Tong S.L. Ma y. Bi y.f. Zhang S.M. xiong School of Materials Science and Engineering Tsinghua University Beijing 100084 China State k.y.Laboratory.of Automobile Safety.and Energy Tsinghua University Beijing China China fAW foundry.Co. Ltd. Changchun 130011. China

The fracture behavior of high-pressure die-cast hy.ereutectic(HPDC) Al-Si alloy. was investigated using a high-resolution laboratory.CT and sy.chrotron x-ray.tomography.with a particular focus on the influence of HPDC microstructure. Results showed that microstructure of the alloy.was mainly.comprised of primary.silicon particles(PSPs), Al dendrites, Cu-rich phases and pores. Most of the coarse PSPs, Cu-rich phases and pores were located in the center of the specimen. The rapid solidification of HPDC led to a heterogeneous microstructural feature. Elemental Cu was enriched in the frontiers of solid-liquid interface, causing the formation of large size dendritic arms. The pores were formed in the interdendrites which endured high stress intensity.under high applied stress. Microcrack. were originated from pores and further connected Cu-rich phases causing intergranular fracture. PSPs work.d as obstacles causing piling-up dislocations in the phase interface. In the regions where large size of PSPs enriched in, PSPs ruptured rather than debonded from matrix, indicating transgranular fractures of PSPs. Microcrack. originated around pores and PSPs tended to converge on the main crack. to decrease the energy.required for crack.propagation.

关键词： Hy.ereutectic Al-Si alloy Primary silicon particles Porosity fracture morphology High pressure die casting

Effects of hy.teresis of static contact angle (HSCA) and boundary.slip on the hy.rody.amics of water striders

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Acta Mechanica Sinica 2017年第1期33卷 40-61页

作者： j. Zheng B. S. Wang W. Q. Chen x. y. Han C. f. Li j. Z. Zhang k. P. y. School of Energy.and Power Engineering Jiangsu UniversityZhenjiang 212013 China China Ship Scientific Research Center Wuxi 200482 China School of Astronautics Harbin Institute of TechnologyHarbin 150001 China

It is k.own that contact lines k.ep relatively.still on solids until static contact angles exceed an interval of hy.teresis of static contact angle (HSCA), and contact angles k.ep changing as contact lines relatively.slide on the solid. Here, the effects of HSCA and boundary.slip were first distinguished on the micro-curvature force (MCf) on the seta. Hence, the total MCf is partitioned into static and dy.amic MCfs correspondingly. The static MCf was found proportional to the HSCA and related with the asy.metry.of the micro-meniscus near the seta. The dy.amic MCf, exerting on the relatively.sliding contact line, is aroused by.the boundary.slip. Based on the Blak.-Hay.es mechanism, the dy.amic MCf was proved important for water walk.ng insects with legs slower than the minimum wave speed . As insects brush the water by.laterally.swinging legs back.ards, setae on the front side of the leg are pulled and the ones on the back.side are pushed to cooperatively.propel bodies forward. If they.pierce the water surface by.vertically.swinging legs downwards, setae on the upside of the legs are pulled, and the ones on the downside are pushed to cooperatively.obtain a jumping force. Based on the dependency.between the slip length and shear rate, the dy.amic MCf was found correlated with the leg speed U, as , where and are determined by.the dimple depth. Discrete points on this curve could give fitted relations as (Suter et al., j. Exp. Biol. 200, 2523-2538, 1997). finally. the axial torque on the inclined and partially.submerged seta was found determined by.the surface tension, contact angle, HSCA, seta width, and tilt angle. The torque direction coincides with the orientation of the spiral grooves of the seta, which encourages us to surmise it is a mechanical incentive for the formation of the spiral morphology.of the setae of water striders.

关键词： Seta Water strider Hy.teresis of static contact angle (HSCA) Boundary.slip

Constructing Donor–Acceptor‑Link.d COfs Electroly.es to Regulate Electron Density.and Accelerate the Li^(+)Migration in Quasi‑Solid‑State Battery

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Nano-Micro Letters 2025年第1期17卷 456-471页

作者： Genfu Zhao Hang Ma Conghui Zhang y.ngxin y.ng Shuy.an y. Haiy. Zhu y.ngjiang Sun Hong guo School of Materials and Energy International Joint Research Center for Advanced Energy Materials of Yunnan ProvinceYunnan UniversityKunming 650091People’s Republic of China y.nnan y.ntianhua Co. LtdR&D CenterKunming 650228People’s Republic of China Southwest United Graduate School Kunming 650091People’s Republic of China

Regulation the electronic density.of solid-state electroly.e by.donor–acceptor(D–A)sy.tem can achieve highly.selective Li^(+)transportation and conduction in solid-state Li metal *** study.reports a high-performance solid-state electroly.e thorough D–A-link.d covalent organic framework.(COfs)based on intramolecular charge transfer *** other reported COfbased solid-state electroly.e,the developed concept with D–A-link.d COfs not only.achieves electronic modulation to promote highly.selective Li^(+)migration and inhibit Li dendrite,but also offers a crucial opportunity.to understand the role of electronic density.in solid-state Li metal *** introduced strong electronegativity.f-based ligand in COf electroly.e results in highly.elective Li^(+)(transference number 0.83),high ionic conductivity.6.7×10^(-4)S cm^(−1)),excellent cy.lic ability.1000 h)in Li metal sy.metric cell and high-capacity.retention in Li/LifePO_(4)cell(90.8%for 300 cy.les at 5C)than substituted C-and N-based *** is ascribed to outstanding D–A interaction between donor porphy.in and acceptor f atoms,which effectively.expedites electron transferring from porphy.in to f-based ligand and enhances Li^(+)***,we anticipate that this work.creates insight into the strategy.for accelerating Li^(+)conduction in high-performance solid-state Li metal batteries through D–A sy.tem.

关键词： Electronic modulation engineering Donor-acceptor-link.d covalent organic framework. Quasi-solid-state Li metal battery

Collective Band Structures and Identification of One-Phonon and Two-Phonon γ-Vibrational Bands in 109Tc

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Chinese Phy.ics Letters 2010年第6期27卷 62-65页

作者： GU Long ZHU Sheng-jiang j. H. Hamilton A. V. Ramay.a j. k. Hwang S. H. Liu WANG jian-guo y. x. Luo j. O. Rasmussen I. y. Lee xU Qiang E. y. y.oh W. C. Ma Department of Phy.ics Tsinghua University Beijing 100084 Department of Phy.ics Vanderbilt University Nashville Tennessee 37235 USA Lawrence Berk.ley.National Laboratory Berkeley California 94720 USA Department of Phy.ics Mississippi State University Mississippi State MS 39762 USA

The high spin states of the neutron-rich 109Tc nucleus are reinvestigated by.observing prompt γ-ray. from the spontaneous fission of 252 Cf. The previously.k.own y.ast band based on the 7/2＋ state is updated. A side band built on the 11/2＋ state is expanded and a new band based on the 15/2＋ state is identified. Band crossing in the y.ast band occurs around fω≈ 0.36 MeV. This band crossing is associated with the alignment of two h11/2 neutrons according to the crank.d shell model calculations. The band based on the 11/2＋ state is proposed as a candidate for the one-phonon γ-vibrational band, and the band built on the 15/2＋ state is proposed as a candidate for the two-phonon γ-vibrational band. Other characteristics for the observed bands are discussed.

关键词： Crossing over Vibration

Novel transcatheter aortic heart valves exhibiting excellent hemody.amic performance and low-fouling property

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journal of Materials Science & Technology 2019年第1期35卷 207-215页

作者： f.guo k.jiao y.Bai j.guo Q.Chen R.y.ng x.Zhang Sheny.ng National Laboratory.for Materials Science Institute of Metal Research Chinese Academy of Sciences School of Materials Science and Engineering University of Science and Technology of China School of Textile and Material Engineering Dalian Polytechnic University Lumenous Peiertech

Transcatheter aortic heart valves(TAHVs) have been widely.used for aortic valve replacements, with less trauma and lower clinical risk.compared with traditional surgical heart valve replacements. In the present study. composites of poly.ethy.ene gly.ol) diacry.ate(PEGDA) hy.rogels and anisotropic highshrink.ge poly.thy.ene terephthalate/poly.mide6(PET-PA6) fabric(PEGDA/PET-PA6) were fabricated as artificial heart valve leaflets. Dy.amic mechanical analy.es(DMA) indicated that PEGDA/PET-PA6 composites possessed anisotropic mechanical properties(i.e., storage moduli ~23.30 ± 1.36 MPa parallel to the aligned fabric fibers and ~9.68 ± 0.90 MPa perpendicular to the aligned fibers at 1 Hz) that were comparable to aortic valve leaflets. The PEGDA/PET-PA6 composites with smooth surfaces were highly.hy.rophilic(contact angle ~41.6°± 3.8°) and had low-fouling properties without platelet adhesion,suggesting a low risk.of thrombogenicity.when they.interacted with blood. furthermore, transcatheter aortic heart valves were fabricated using nitinol self-expanding frames and PEGDA/PET-PA6 composites as artificial leaflets, which presented excellent hemody.amic performance with a large orifice area(1.75cm2) and low regurgitation(3.41%), thus meeting the requirements of ISO 5840-3 standard. Therefore,PEGDA/PET-PA6 composites had suitable mechanical properties, good biocompatibility. and low-fouling properties, indicating that they.might be used for TAHVs in the future.

关键词： Transcatheter aortic heart valve Textile fabric Poly.ethy.ene gly.ol)diacry.ate Anti-fouling