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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

Influence of lanthanum as additive and post-treatment on the corrosion protection properties and surface morphology of mild steel chemically treated by a cerium conversion coating

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Journal of Rare Earths 2018年第10期36卷 1112-1120页

作者： z.Mahidashti b.Ramezanzadeh Department of Surface Coatings and Corrosion Institute for Color Science and Technology (ICST)

The influence of cerium conversion coating（CeCC） modified by lanthanum in two forms of additive and post-treatment solution on the corrosion resistance, surface morphology and surface chemistry of the mild steel was studied. Corrosion resistance was evaluated by electrochemical impedance spectroscopy,while the scanning electron microscopy, X-ray photoelectron spectroscopy and contact angle test were employed to investigate the surface characteristics. Results reveal that the CeCC post-treated by lanthanum containing solution gives rise to the deposition of a crack free and uniform conversion coating with enhanced corrosion resistance on the steel surface. Also, the surface free energy is increased after post-treatment.

关键词： Surface treatment Corrosion resistance XPS AFM SEM/EDS Surface free energy

NUMERICAL SIMULATION OF TEMPERATURE FIELDS IN ELECTROSLAG REMELTING SLAb INGOTS

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Acta Metallurgica Sinica(English Letters) 2008年第4期21卷 253-259页

作者： L.z. Chang b.z. Li Department of Metallurgical Technology Central Iron ＆ Steel Research Institute Beijing 100081 China

The method based on transient heat transfer model is adopted to simulate electro-slag remelting process. The calculated results of the model show that the process is in the quasi-steady state, and the shape of pool remains unchanged when the height of ingot is approximately 2.5-3 times the thickness of slab ingot. The change in the shape of pool is found to be strongly dependent on the pattern of melting rate, and hence, the power input; the depth of the molten pool increases with the increase in melting speed. It is concluded that a transient heat transfer model has to be used to obtain reliable input information for the entire, operatina time.

关键词： ESR Slab ingot Mathematical model Shape of molten metal pool

A prediction model for the effective thermal conductivity of nanofluids considering agglomeration and the radial distribution function of nanoparticles

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Acta Mechanica Sinica 2018年第3期34卷 507-514页

作者： z.M.zheng b.Wang School of Physics Sun Yat-Sen UniversityGuangzhou 510275China Instimt Franco-Chinois de l'Energie Nucleaire Sun Yat-Sen UniversityZhuhai 519000China

Conventional heat transfer fluids usually have low thermal conductivity, limiting their efficiency in many applications. Many experiments have shown that adding nanosize solid particles to conventional fluids can greatly enhance their thermal conductivity. To explain this anomalous phenomenon, many theoretical investigations have been conducted in recent years. Some of this research has indicated that the particle agglomeration effect that commonly occurs in nanofluids should play an important role in such enhancement of the thermal conductivity, while some have shown that the enhancement of the effective thermal conductivity might be accounted for by the structure of nanofluids, which can be described using the radial distribution function of particles. However, theoretical predictions from these studies are not in very good agreement with experimental results. This paper proposes a prediction model for the effective thermal conductivity of nanofluids, considering both the agglomeration effect and the radial distribution function of nanoparticles. The resulting theoretical predictions for several sets of nanofluids are highly consistent with experimental data.

关键词： Nanofluid Thermal conductivity Modeling Agglomeration Radial distribution function

Strain-induced formation of a gradient nanostructured surface layer on an ultrahigh strength bearing steel

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Journal of Materials Science & Technology 2018年第9期34卷 1676-1684页

作者： K.zhang z.b.Wang Shenyang National Laboratory for Materials Science Institute of Metal Research Chinese Academy of SciencesShenyang 110016 China University of Chinese Academy of Sciences Beijing 100049 China

In the present work, an ultrahigh strength bearing steel（AISI 52100） was subjected to surface mechanical rolling treatment（SMRT） at room temperature. Microstructural observations showed that martensitic laths, twins and cementite particles in the initial microstructure underwent distinct plastic strains and were gradually refined into nanostructures. Consequently, a gradient nanostructured（GNS） surface layer with a mean grain size of -24 nm at the top surface was obtained on the bearing steel, resulting in an increment of -20% in the surface hardness. Analyses based on microstructural evolution, phase constitution and in-depth hardness distribution revealed a mechanically induced formation mechanism of the GNS surface layer. The multiple surface severe plastic deformation under fine lubrication and cooling during SMRT contributed to the formation of a thick hardened surface layer on the bearing steel.

关键词： Gradient nanostructured Ultrahigh strength bearing steel Plastic deformation Martensite Surface mechanical rolling treatment

Dispersion and Damage of Carbon Nanotubes in Carbon Nanotube/7055Al Composites During High-Energy ball Milling Process

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Acta Metallurgica Sinica(English Letters) 2021年第2期34卷 196-204页

作者： S.bi b.L.Xiao z.H.Ji b.S.Liu z.Y.Liu z.Y.Ma Shi-changxu Innovation Center for Advanced Materials Institute of Metal ResearchChinese Academy of Sciences72 Wenhua RoadShenyang 110016China School of Material Science and Engineering University of Science and Technology of China72 Wenhua RoadShenyang 110016China AVIC Manufacturing Technology Institute Beijing 100024China

High-energy ball milling(HEbM)combined with powder metallurgy route was used to fabricate carbon nanotube(CNT)reinforced 7055 Al *** powder morphology evolution processes(HEbM-1 and HEbM-2)were designed to investigate the dispersion and damage of CNTs during HEbM ***-1 evolution process involved powder fl attening,cold-welding and fracture,while HEbM-2 evolution process consisted of powder fl attening and *** HEbM-1,the repetitive fracture and cold-welding process was effective for dispersing ***,the powder fl attening process in HEbM-2 was unsuccessful in dispersing CNTs due to two reasons:(1)the thickness of fl aky Al powders exceeded the critical value,and(2)the clustered CNTs embedded in fl aky Al powders could not be *** of the broadening of D band and the appearance of a new defect-related D’band,product of I D/I G and full width half maximum of D band,rather than I D/I G,was used to evaluate the actual damage of *** indicates that the damage of CNTs was severe in powder fl attening and fracture stages,while the damage of CNTs was small in powder cold-welding stage.

关键词： Metal matrix composites Carbon nanotubes Powder evolution Dispersion and damage Powder metallurgy

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

The xanthate route to all-carbon quaternary centers

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Science China Chemistry 2019年第11期62卷 1450-1462页

作者： béatrice Quiclet-Sire Samir z.zard Laboratoire de Synthèse Organique Ecole Polytechnique

This review discusses the numerous routes to all-carbon quaternary centers based on the unique radical chemistry of xanthates. Itsummarizes the various approaches to the synthesis of tertiary xanthates then describes the intra- and intermolecular radicaladditions and combinations thereof that have so far been used to construct quaternary centers.

关键词： xanthates quaternary centers radical addition cyclization tandem reactions

Crystal Structure of 5-(l-Menthyloxy)-3-bromo-4-(R)-(+)-Methylbenzylamino-2(5H)-Furanone

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Chinese Journal of Structural Chemistry 1999年第2期18卷 32-34页

作者： Geng, z Huang, b Chen, QH Capital Normal Univ Dept Chem Beijing 100037 Peoples R China beijing Normal Univ Dept Chem Beijing 100875 Peoples R China

The crystal structure of the title compound 1, C 22 H 30 brNO 3, was determined by X ray analysis at 296(1)K. The crystal belongs to othorhombic system, space group P2 12 12 1 with a=9.842(5), b=12.510(5), c=17.763(6) , V=2187(3)  3, z=4, M r=436.37, D x =1.33 g/cm 3, μ =18.79 cm 1 , F(000) =912 and the final R=0.047 and R w=0.053 for 1429 observed reflections with I≥3σ(I). Structure analysis reveals that the absolute configuration at C 14 of the acetal carbon of the title compound is S.

关键词： crystal structure 2(5H) furanone absolute configuration.