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On the topological number in Kelvin's circulation of inviscid fluids

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Communications in Theoretical Physics 2024年第12期76卷 176-180页

作者： z B Guo State Key Laboratory of Nuclear Physics and Technology School of Physics Peking University

Kelvin's circulation,as a loop integral of the velocity field,is first shown to be equal to Γc=2πΔnΓ1+constant in an inviscid fluid,with Γ1a unit *** integer Δn is interpreted as the number of net 27r-rotations of the velocity vector in one cyclicality along the circulation loop and hence it is a topological *** from the linkage number in the helicity invariant,which only exists in 3D space,the topological number in the circulation invariant is independent of the spatial dimension.A further study reveals that this new topological phase 2πΔn is rooted at the gauge invariance of the circulation and it is a counterpart of the Berry's phase in the quantum system.

关键词： Berry's phase fluids Kelvin’s circulation topological number

Fire hazard in transportation infrastructure:Review,assessment,and mitigation strategies

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Frontiers of Structural and Civil Engineering 2021年第1期15卷 46-60页

作者： Venkatesh KODUR M.z.NASER Department of Civil and Environmental Engineering Michigan State UniversityEast LansingMI 48824-1226USA Glenn Department of Civil Engineering Clemson UniversityClemsonSC 29634USA

This paper reviews the fire problem in critical transportation infrastructures such as bridges and *** magnitude of the fire problem is illustrated,and the recent increase in fire problems in bridges and tunnels is *** research undertaken to address fire problems in transportation structures is reviewed,as well as critical factors governing the performance of those ***,key strategies recommended for mitigating fire hazards in bridges and tunnels are presented,and their applicability to practical situations is demonstrated through a practical case ***,research needs and emerging trends for enhancing the“state-of-the-art”in this area are discussed.

关键词： fire hazard bridges tunnels fire resistance mitigation strategies transportation infrastructure

Precipitation of multi-type nano-quasicrystals in a Mg-zn-Y alloy

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Journal of Magnesium and Alloys 2024年第3期12卷 997-1008页

作者： W.z.Wang X.z.zhou L.F.zhang H.Q.Ye z.Q.Yang Shenyang National Laboratory for Materials Science Institute of Metal ResearchChinese Academy of ScienceShenyang 110016China Ji Hua Laboratory Foshan 528251China Foshan University Foshan 528231China

Mg-6zn-1Y(at.%)ribbons with strengthening precipitates of multi-type nanoquasicrystals were prepared by melt-spinning followed by aging *** evolution of the rapidly solidified ribbons during isothermal aging was comprehensively studied using various electron microscopy *** new kinds of decagonal quasicrystals were formed in aged ribbons,in addition to precipitation of nanometer icosahedral ***-resolution observations reveal that both decagonal quasicrystals can be modeled by quasiperiodic tiling with decagonal clusters of 2.5 nm in diameter,but overlap of neighboring clusters in both decagonal quasicrystals is different from the Gummelt model observed in other quasicrystals.A shell composed of complex Laves Mg-zn domains was formed surrounding each decagonal quasicrystal precipitate upon prolonged *** addition,all kinds of nanoprecipitates exhibit excellent structure and size stability at 573 *** findings may have implications for not only fundamental studies about quasicrystals,but also microstructural manipulation of high-performance Mg alloys.

关键词： Quasicrystal Mg alloys Rapid solidification Scanning-transmission electron microscopy.

Centrality of the collision and random matrix theory

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Chinese Physics C 2010年第10期34卷 1593-1597页

作者： z.Wazir Department of Physics COMSATS Institute of Information Technology

I discuss the results from a study of the central ^12CC collisions at 4.2 A GeV/c. The data have been analyzed using a new method based on the Random Matrix Theory. The simulation data coming from the Ultra Relativistic Quantum Molecular Dynamics code were used in the analyses. I found that the behavior of the nearest neighbor spacing distribution for the protons, neutrons and neutral pions depends critically on the multiplicity of secondary particles for simulated data. I conclude that the obtained results offer the possibility of fixing the centrality using the critical values of the multiplicity.

关键词： random matrix theory UrQMD central collisions multiplicity

Opportunities and challenges of biodegradable zn-based alloys

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Journal of Materials Science & Technology 2020年第11期42卷 136-138页

作者： H.F.Li z.z.Shi L.N.Wang Beijing Advanced Innovation Center for Materials Genome Engineering School of Materials Science and EngineeringUniversity of Science and Technology BeijingBeijing100083China

Following the footsteps of biodegradable Mg-based and Fe-based alloys,biodegradable zn-based alloy is a newcomer and rising star in the family of biodegradable metals and *** combined superior mechanical properties,appropriate degradation rates,excellent biocompatibility of biodegradable zn-based alloys have brought worldwide research interest on the design,development and clinical translation of zn-based *** present perspective has summarized opportunities and challenges in the development of biodegradable zn-based alloys.

关键词： Biodegradable zn-based alloys Clinical applications Mechanical properties Degradation behavior Biocompatibility Corrosion fatigue Bio-tribocorrosion

Discrete-frequency Convergence of Iterative Learning Control for Linear Time-invariant systems with Higher-order Relative Degree

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International Journal of Automation and computing 2015年第3期12卷 281-288页

作者： Xiao-E Ruan zhao-zhen Li z.z.Bien School of Mathematics and Statistics Xi an Jiaotong University Department of Electrical Engineering Korea Advanced Institute of Science and Technology

In this paper, a discrete-frequency technique is developed for analyzing sufficiency and necessity of monotone convergence of a proportional higher-order-derivative iterative learning control scheme for a class of linear time-invariant systems with higher-order relative degree. The technique composes of two steps. The first step is to expand the iterative control signals, its driven outputs and the relevant signals as complex-form Fourier series and then to deduce the properties of the Fourier coefficients. The second step is to analyze the sufficiency and necessity of monotone convergence of the proposed proportional higher-order-derivative iterative learning control scheme by assessing the tracking errors in the forms of Paserval s energy modes. Numerical simulations are illustrated to exhibit the validity and the effectiveness.

关键词： Iterative learning control monotone convergence discrete frequency-domain spectrum Fourier series Parseval s energy equality rel

FINITE ELEMENT ANALYSIS FOR MICROSTRUCTURE EVOLUTION IN HOT FINISHING ROLLING OF STEEL STRIPS

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Acta Metallurgica Sinica(English Letters) 2007年第2期20卷 79-86页

作者： z.D. Qu S.H. zhang D.z. Li z.T. Wang Institute of Metal Research Chinese Academy of Sciences Shenyang 110016 China College of Material Science and Engineering Taiyuan University of Science andTechnology Taiyuan 030024 China Shenyang Ligong University Shenyang 110168 China

A computer model that describes the evolution of microstructures during the hot finishing rolling of SS400 steel has been proposed. It has been found that the microstructure strongly depends on processing of materials and on their parameters, which affected the history of the thermomechanical variables, such as temperature, strain, and strain rate. To investigate the microstructural evolutions during the hot finishing rolling process, the rigid-thermoviscoplastic finite element method （FEM） has been combined with dynamic recrystallization, static recrystallization, and grain growth models. The simulation results show a good agreement with those from the prediction software online.

关键词： finite element method (FEM) finishing rolling microstructure evolution recrystallization

Kinetic Parameters Estimation of MgO-C Refractory by Shrinking Core Model

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Journal of Materials Science & Technology 2006年第6期22卷 826-832页

作者： B.Hashemi z.A.Nemati S.K.Sadrnezhaad z.A.Moghimi Department of Materials Science School of EngineeringShiraz UniversityShirazIran Department of Materials Science and Engineering Sharif University of TechnologyTehran 11365-9466Iran

Kinetics of oxidation of MgO-C refractories was investigated by shrinking core modeling of the gas-solid reactions taking place during heating the porous materials to the high temperatures. Samples containing 4.5-17 wt pct graphite were isothermally oxidized at 1000-1350℃. Weight loss data was compared with predictions of the model. A mixed 2-stage mechanism comprised of pore diffusion plus boundary layer gas transfer was shown to generally control the oxidation rate. Pore diffusion was however more effective, especially at graphite contents lower than 10 wt pct under forced convection blowing of the air. Model calculations showed that effective gas diffusion coefficients were in the range of 0.08 to 0.55 cm^2/s. These values can be utilized to determine the corresponding tortuosity factors of 6.85 to 2.22. Activation energies related to the pore diffusion mechanism appeared to be around （46.44±2） kJ/mol. The estimated intermolecular diffusion coefficients were shown to be independent of the graphite content, when the percentage of the graphite exceeded a marginal value of 10.

关键词： Modeling Kinetics MgO-C Oxidation Diffusion coefficient

Asymptotic Properties of Parabolic Systems for Null-Recurrent Switching Diffusions

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Acta Mathematicae Applicatae Sinica 2007年第2期23卷 177-194页

作者： R.z.Khasminskii Department of Mathematics Wayne State University Detroit MI 48202 USA.

This work is concerned with the asymptotic behavior of systems of parabolic equations arising from null-recurrent switching diffusions, which are diffusion processes modulated by continuous-time Markov chains. A sufficient condition for null recurrence is presented. Moreover, convergence rate of the solutions of systems of homogeneous parabolic equations under suitable conditions is established. Then a case study on verifying one of the conditions proposed is provided with the use of a two-state Markov chain. To verify the condition, boundary value problems （BVPs） for parabolic systems are treated, which are not the usual two-point BVP type. An extra condition in the interior is needed resulting in jump discontinuity of the derivative of the corresponding solution.

关键词： Parabolic system switching diffusion null recurrence Markov chain