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Magnetic skyrmions:intriguing physics and new spintronic device concepts

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National Science Review 2019年第2期6卷 210-212页

作者： yan zhou School of Science and Engineering The Chinese University of Hong Kong

The mathematical concept of skyrmions was first introduced by high-energy physicist Tony Skyrme in 3D space for describing the stability of hadrons as objects possessing non-trivial topological numbers in a non-linear sigma model. Later on, the original concept of skyrmions was generalized to various condensed-matter systems such as

关键词： Magnetic skyrmions:intriguing physics and new spintronic device concepts DMI

Double Hopf bifurcation of composite laminated piezoelectric plate subjected to external and internal excitations

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Applied Mathematics and Mechanics(English Edition) 2017年第5期38卷 689-706页

作者： yan zhou Wei ZHANG Mathematics Science College Inner Mongolia Normal University Beijing Key Laboratory on Nonlinear Vibrations and Strength of Mechanical Structures College of Mechanical EngineeringBeijing University of Technology

The double Hopf bifurcation of a composite laminated piezoelectric plate with combined external and internal excitations is studied. Using a multiple scale method, the average equations are obtained in two coordinates. The bifurcation response equations of the composite laminated piezoelectric plate with the primary parameter resonance, i.e., 1：3 internal resonance, are achieved. Then, the bifurcation feature of bifurcation equations is considered using the singularity theory. A bifurcation diagram is obtained on the parameter plane. Different steady state solutions of the average equations are analyzed. By numerical simulation, periodic vibration and quasi-periodic vibration responses of the Composite laminated piezoelectric plate are obtained.

关键词： double Hopf bifurcation composite laminated piezoelectric plate periodic solution quasi-periodic solution

On Tame Kernels and Ideal Class Groups

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Acta Mathematica Sinica,English Series 2007年第10期23卷 1807-1812页

作者： Hai yan zhou Department of Mathematics Nanjing University Nanjing 210093 P. R. China Institute of Mathematics School of Mathematics and Computer Sciences Nanjing Normal University Nanjing 210097 P. R. China

It is well known that there is a close connection between tame kernels and ideal class groups of number fields. However, the latter is a very difficult subject in number theory. In this paper, we prove some results connecting the p^n-rank of the tame kernel of a cyclic cubic field F with the p^n-rank of the coinvariants of μp^n×CI（δE,T） under the action of the Galois group, where E = F（ζp^n ） and T is the finite set of primes of E consisting of the infinite primes and the finite primes dividing p. In particular, if F is a cyclic cubic field with only one ramified prime and p = 3, n = 2, we apply the results of the tame kernels to prove some results of the ideal class groups of E, the maximal real subfield of E and F（ζ3）.

关键词： cyclic cubic fields tame kernels ideal class groups

Sub-50 nm optical imaging in ambient air with 10× objective lens enabled by hyper-hemi-microsphere

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Light(Science & Applications) 2023年第3期12卷 398-408页

作者： Guangxing Wu yan zhou Minghui Hong Department of Electrical and Computer Engineering National University of Singapore4 Engineering Drive 3Singapore117576Singapore School of Aerospace Engineering Xiamen UniversityXiamen361005China Present address:Peng Cheng Laboratory Shenzhen518055China

Optical microsphere nanoscope has great potential in the inspection of integrated circuit chips for semiconductor industry and morphological characterization in biology due to its superior resolving power and label-free ***,its resolution in ambient air is restricted by the magnification and numerical aperture(NA)of *** magnification objective lens is required to be coupled with microsphere for nano-imaging beyond the diffraction *** overcome these challenges,in this work,high refractive index hyper-hemi-microspheres with tunable magnification up to 10×are proposed and realized by accurately tailoring their thickness with focused ion beam(FIB)*** effective refractive index is put forward to guide the design of *** demonstrate that the imaging resolution and contrast of a hyper-hemi-microsphere with a higher magnification and larger NA excel those of a microsphere in ***,the hyper-hemi-microsphere could resolve~50 nm feature with higher image fidelity and contrast compared with liquid immersed high refractive index *** a hyper-hemi-microsphere composed microscale compound lens configuration,sub-50 nm optical imaging in ambient air is realized by only coupling with a 10×objective lens(NA=0.3),which enhances a conventional microscope imaging power about an order of magnitude.

关键词： ambient immersed refractive

Atomically dispersed copper species on ceria for the low-temperature water-gas shift reaction

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Science China Chemistry 2021年第7期64卷 1103-1110页

作者： Jing Ning yan zhou Wenjie Shen State Key Laboratory of Catalysis Dalian Institute of Chemical PhysicsChinese Academy of SciencesDalian 116023China University of Chinese Academy of Sciences Beijing 100049China

The structure of copper species,dispersed on nanostructured ceria(particles,rods and cubes),was analyzed by scanning transmission electron microscopy(STEM)and X-ray photoelectron spectroscopy(XPS).It was interestingly found that the density of surface oxygen vacancies(or defect sites),induced by the shape of ceria,determined the geometrical structure and the chemical state of copper *** dispersed species and monolayers containing few to tens of atoms were formed on ceria particles and rods owing to the enriched anchoring sites,but copper clusters/particles co-existed,together with the highly dispersed atoms and monolayers,on cubic *** atomically dispersed copper sites and monolayers interacted strongly with ceria,involving a remarkable charge transfer from copper to ceria at their *** activity for the low-temperature watergas shift reaction of the Cu/CeO_(2) catalysts was associated with the fraction of the positively-charged copper atoms,demonstrating that the active sites could be tuned by dispersing Cu species on shape-controlled ceria particles.

关键词： Cu/CeO_(2)catalysts ceria shape copper-ceria interface atomically dispersed copper sites monolayers low-temperature water-gas shift reaction

SIMULATION OF THERMAL TRANSPORT IN AQUIFER:A GWHP SYSTEM IN CHENGDU,CHINA

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Journal of Hydrodynamics 2009年第5期21卷 647-657页

作者： zhou yan-zhang zhou Zhi-fang Institute of Groundwater Science and Engineering Hohai University Nanjing 210098 China

With an established convection-dispersion model for the thermal transport in aquifer, the thermal transport processes in an unconfined aquifer of a Groundwater Heat Pump （GWHP） system in Chengdu, China, are simulated with double-well intervals and cooling-load design fluctuations in summer running period under special groundwater flow and heat source conditions, and the stage-characteristics of the thermal transport in the aquifer are investigated in the running cycle （1 year） numerically. The results show that the thermal transport in the aquifer is closely related to the distance between pumping and injecting wells and the cooling-load design fluctuations, especially, to the cycling water volume. The thermal transport in the aquifer sees different characteristics in the two states in the pumping-recharging stages in summer/winter and the storing stages in spring/autumn. With the hydro-geologic theory and the numerical model, the effect of the groundwater-flow on the thermal transport in the unconfined aquifer is discussed.

关键词： Groundwater Heat Pump (GWHP) thermal transport in aquifer numerical simulation groundwater flow

A New Interface Identification Technique Based on Absolute Density Gradient for Violent Flows

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Computer Modeling in Engineering & Sciences 2018年第5期115卷 131-147页

作者： yan zhou Qingwei Ma School of Mathematics Computer Science and EngineeringCity University LondonNorthampton SquareLondonEC1V 0HB

An identification technique for sharp interface and penetrated isolated particles is developed for simulating two-dimensional,incompressible and immiscible two-phase flows using meshless particle methods in this *** technique is based on the numerically computed density gradient of fluid particles and is suitable for capturing large interface deformation and even topological changes such as merging and breaking up of phases.A number of assumed particle configurations will be examined using the technique,including these with different level of randomness of particle *** tests will show that the new technique can correctly identify almost all the interface and isolated particles,and also show that it is better than other existing popular methods tested.

关键词： Meshless method Particle method two-phase flow interface identification violent flows breaking waves

A NONMONOTONE SECOND-ORDER STEPLENGTH METHOD FOR UNCONSTRAINED MINIMIZATION

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Journal of Computational Mathematics 2007年第1期25卷 104-112页

作者： Qun-yan zhou Wen-yu Sun Department of Basic Science Jiangsu Teachers University of Technology Changzhou 213001 China School of Mathematics and Computer Science Nanjing Normal University Nanjin9 210097 China School of Mathematics and Computer Science Nanjing Normal University Nanjing 210097 China

In this paper, a nonmonotone method based on McCormick＇s second-order Armijo＇s step-size rule [7] for unconstrained optimization problems is proposed. Every limit point of the sequence generated by using this procedure is proved to be a stationary point with the second-order optimality conditions. Numerical tests on a set of standard test problems are presented and show that the new algorithm is efficient and robust.

关键词： Nonmonotone method Armijo's line search Direction of negative curvature,Unconstrained optimization.

AN ADAPTIVE NONMONOTONIC TRUST REGION METHOD WITH CURVILINEAR SEARCHES

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Journal of Computational Mathematics 2006年第6期24卷 761-770页

作者： Qun-yan zhou Wen-yu Sun School of Mathematics and Computer Science Nanjing Normal University Nanjing 210097 China Department of Mathematics Jiangsu Teacher University of Technology Changzhou 213001 China

In this paper, an algorithm for unconstrained optimization that employs both trust region techniques and curvilinear searches is proposed. At every iteration, we solve the trust region subproblem whose radius is generated adaptively only once. Nonmonotonic backtracking curvilinear searches are performed when the solution of the subproblem is unacceptable. The global convergence and fast local convergence rate of the proposed algorithms are established under some reasonable conditions. The results of numerical ＇experiments are reported to show the effectiveness of the proposed algorithms.

关键词： Unconstrained optimization Preconditioned gradient path Trust region method,Curvilinear search.