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Assessing workability of greased bearings after long-term storage

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Friction 2019年第5期7卷 489-496页

作者： Michael VARENBERG yuri kligerman Grigory HALPERIN Saad NAKAD Haytam KASEM George W.Woodruff School of Mechanical Engineering Georgia Institute of TechnologyAtlantaGA30332USA Department of Mechanical Engineering Technion-Israel Institute of TechnologyHaifa32000Israel Department of Mechanical Engineering Azrieli College of EngineeringJerusalem9103501Israel

Here, we developed a technique to assess the workability of sealed-for-life greased rolling bearings after a long-term storage. In this framework, we devised a model of equivalent transition between the conditions of natural ageing under daily and seasonally fluctuating temperature, and the conditions of accelerated thermal ageing at a constant high temperature. The tested bearings were thermally aged, and then their steady state friction and outer ring temperature were examined in a custom high-speed spindle. These results were compared to the performance of a reference new bearing tested under the same loading conditions. Our findings suggest that long-term storage can significantly degrade the performance of sealed-for-life greased rolling bearings. However, a proper running-in can substantially deter the ageing-driven degradation of the bearings.

关键词： grease lubrication ball bearings thermal ageing lubricant degradation

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All-dielectric meta-optics and non-linear nanophotonics

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National Science Review 2018年第2期5卷 144-158页

作者： yuri Kivshar Nonlinear Physics Center Australian National University ITMO University

Most optical metamaterials fabricated and studied to date employ metallic components resulting in significant losses, heat and overall low efficiencies. A new era of metamaterial physics is associated with all-dielectric meta-optics, which employs electric and magnetic Mie resonances of subwavelength particles with high refractive index for an optically induced magnetic response, thus underpinning a new approach to design and fabricate functional and practical metadevices. Here we review the recent developments in meta-optics and subwavelength dielectric photonics and demonstrate that the Mie resonances can play a crucial role in the realization of the unique functionalities of meta-atoms, also driving novel effects in the fields of metamaterials and nanophotonics. We discuss the recent research frontiers in all-dielectric meta-optics and uncover how Mie resonances can be employed for a flexible control of light with full phase and amplitude engineering, including unidirectional metadevices, highly transparent metasurfaces,non-linear nanophotonics and topological photonics.

关键词： nanophotonics Mie resonances meta-optics metasurfaces metamaterials

Approximations of the Fractional Integral and Numerical Solutions of Fractional Integral Equations

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Communications on Applied Mathematics and Computation 2021年第3期3卷 545-569页

作者： yuri Dimitrov Department of Mathematics and Physics University of Forestry1756 SofiaBulgaria Institute of Mathematics and Informatics Bulgarian Academy of Sciences1113 SofiaBulgaria

In the present paper,we derive the asymptotic expansion formula for the trapezoidal approximation of the fractional *** use the expansion formula to obtain approximations for the fractional integral of ordersα,1+α,2+α,3+αand 4+α.The approximations are applied for computation of the numerical solutions of the ordinary fractional relaxation and the fractional oscillation equations expressed as fractional integral equations.

关键词： Fractional integral Trapezoidal approximation Fractional integral equation Finite-difference scheme

Strengthening of tungsten by coherent rhenium precipitates formed during low fluence irradiation

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Tungsten 2022年第1期4卷 20-27页

作者： yuri Osetsky Materials Science and Technology Division Oak Ridge National LaboratoryOak RidgeTN 37831USA

Experimental data show that the accumulation of rhenium and osmium from transmutation reactions severely affect the microstructural evolution and property degradation of tungsten-based materials under neutron *** and modeling have confirmed that Re atom transport in W is by irradiation-produced migrating self-interstitial *** this diffusion mode in operation,a specific microstructure evolution is realized when at relatively low neutron fluence the Re-rich precipitates are formed,while the void and interstitial loop population development is suppressed,affecting the mechanical *** research shows the effect of small coherent Re-rich precipitates on the dislocation glide under stress,investigated using the molecular dynamics approach with empirical interatomic *** results are compared with an earlier simulation of void hardening in *** is demonstrated that small coherent Re-rich precipitates of less than 6 nm diameter represent relatively weak obstacles for moving edge *** implication of these results on the interpretation of experimental results is discussed.

关键词： Tungsten-rhenium alloys Molecular dynamics Re-rich precipitates Dislocation obstacle interaction Dislocation dynamics Obstacle strength

Electric resistivity of partially ionized plasma in the lower solar atmosphere

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Research in Astronomy and Astrophysics 2021年第9期21卷 193-201页

作者： Jongchul Chae yuri ELitvinenko Astronomy Program Department of Physics and AstronomySeoul National UniversitySeoul 08826Korea Department of Mathematics University of WaikatoP.B.3105Hamilton 3240New Zealand

The lower solar atmosphere is a gravitationally stratified layer of partially ionized *** calculate the electric resistivity in the solar photosphere and chromosphere,which is the key parameter that controls the rate of magnetic reconnection in a Sweet-Parker current *** calculation takes into account the collisions between ions and hydrogen atoms as well as the electron-ion collisions and the electron-hydrogen atom *** find that under the typical conditions of the quiet Sun,electric resistivity is determined mostly by the electron-hydrogen atom collisions in the photosphere,and mostly by the ion-hydrogen collisions,*** diffusion,in the *** magnetic reconnection events with strong magnetic fields,the ambipolar diffusion,however,may be insignificant because the heating by the reconnection itself may lead to the full ionization of hydrogen *** conclude that ambipolar diffusion may be the most important source of electric resistivity responsible for the magnetic flux cancelation and energy release in chromospheric current sheets that can keep a significant fraction of neutral hydrogen atoms.

关键词： plasmas atomic processes magnetohydrodynamics(MHD) Sun:atmosphere Sun:chromosphere

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Seeing is believing

Light(Science & Applications) 2022年第3期11卷 6-7页

作者： Sergey Krasikov yuri Kivshar Nonlinear Physics Center Research School of PhysicsAustralian National UniversityCanberra ACT 2601Australia and School of Physics and EngineeringITMO UniversitySt.Petersburg197101Russia

Bound states in the continuum are realized in many optical systems as“dark states”,and their presence can be detected in the regime of leaky modes via resonances in *** the authors reveal previously unseen structure... 详细信息

关键词： states dielectric continuum

Air quality short-term control in an industrial region under adverse weather conditions

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Control Theory and Technology 2020年第3期18卷 257-268页

作者： yuri SKIBA David PARRA-CUEVARA Center for Atmospheric Sciences National Autonomous University of MexicoCircuito ExteriorCiudad UniversitariaCDMX04510Mexico

A new short-term optimal control of air quality in an industrial region during atmospheric inversions is *** goal is to prevent violation of health standard of air quality in a few monitored *** control establishes restrictions on the emission rates of industrial sources and includes the identification of the industrial sources violating(exceeding)the emission rates set by the *** control and identification are based on using solutions to an adjoint dispersion *** that show the convergence of the emission rates,prescribed by the control,to the original emission rates of the industrial sources are given(Theorems 4 and 5).These results ensure that the new emission rates of industrial sources(established by the control)will be as close as possible to the original emission rates throughout the entire period of application of the *** creates the minimum possible restrictions on the functioning of industrial *** highlight of the new control is the possibility of selecting special weights for each pollution source in the goal function that is *** weights are mainly aimed at reducing the intensity of emissions of the main sources of *** example demonstrates the ability of the new method.A similar approach can also be used to develop methods for cleaning water zones polluted by oil(the problem of bioremediation),and to prevent excessive pollution of urban areas with automobile emissions.

关键词： Dispersion model adjoint model adjoint estimates optimal control source detection

Meta-optics and bound states in the continuum

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Science Bulletin 2019年第12期64卷 836-842页

作者： Kirill Koshelev Andrey Bogdanov yuri Kivshar Nonlinear Physics Centre Australian National UniversityCanberra ACT 2601Australia ITMO University St. Petersburg 197101Russia

We discuss the recent advances in meta-optics and nanophotonics associated with the physics of bound states in the continuum(BICs). Such resonant states appear due to a strong coupling between leaky modes in optical guiding structures being supported by subwavelength high-index dielectric Mieresonant nanoantennas or all-dielectric metasurfaces. First, we review briefly very recent developments in the BIC physics in application to isolated subwavelength particles. We pay a special attention to novel opportunities for nonlinear nanophotonics due to the large field enhancement inside the particle volume creating the resonant states with high-quality(high-Q) factors, the so-called quasi-BIC, that can be supported by the subwavelength particles. Second, we discuss novel applications of the BIC physics to alldielectric optical metasurfaces with broken-symmetry meta-atoms when tuning to the BIC conditions allows to enhance substantially the Q factor of the flat-optics dielectric structures. We also present the original results on nonlinear high-Q metasurfaces and predict that the frequency conversion efficiency can be boosted dramatically by smart engineering of the asymmetry parameter of dielectric metasurfaces in the vicinity of the quasi-BIC regime.

关键词： Bound states in the continuum Meta-optics Second-harmonic generation Nanoresonator Metasurfaces

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Acoustics of a viscoelastic medium with encapsulated bubbles

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Journal of Hydrodynamics 2021年第1期33卷 55-62页

作者： Damir A.Gubaidullin yuri V.Fedorov Laboratory of Continuum Mechanics Institute of Mechanics and EngineeringFRC Kazan Scientific CenterRussian Academy of SciencesKazanRussia

In this paper,a modified Rayleigh-Lamb equation is derived that takes into account the radial vibrations of a gas bubble coated with a viscoelastic shell and located in an elastic *** small oscillations of inclusion,the problem of heat exchange between a gas,a liquid phase,a viscoelastic shell,and an elastic medium is *** energy integral is *** the case of small disturbances,the dispersion relation is found from the Rayleigh-Lamb equations,energy,and the known wave equation for the bubbly *** analytical expression of the equilibrium speed of sound is written out and its dependence on the size of the viscoelastic shell and the disturbance frequency is *** example of a mixture of polydimethylsiloxane with air bubbles coated with a rubber shell illustrates the influence of the elasticity of the carrier medium and the shell of the bubbles on the dependence of the phase velocity and attenuation coefficient on the perturbation *** a mixture of water with air bubbles coated with a rubber shell,the influence of the dependences of the shear modulus and viscosity of butyl rubber on the frequency of disturbances at different temperature on the dispersion curves is shown.A comparison of the theory with experimental data is given.

关键词： Acoustic wave gas bubbles viscoelastic medium and shell shear modulus dispersion equation