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Global well-posedness of the MHD equations via the comparison principle

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Science China Mathematics 2018年第11期61卷 2111-2120页

作者： dongyi Wei Zhifei Zhang School of Mathematical Sciences Peking University

In this paper,we prove the global well-posedness of the incompressible magneto-hydrodynamics(MHD)equations near a homogeneous equilibrium in the domain R^k×T^(d-k),d≥2,k≥1 by using the comparison principle and cons... 详细信息

关键词： MHD equations comparison principle global well-posedness

Enhanced dissipation for the Kolmogorov flow via the hypocoercivity method Dedicated to Professor Jean-Yves Chemin on the Occasion of His 60th Birthday

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Science China Mathematics 2019年第6期62卷 1219-1232页

作者： dongyi Wei Zhifei Zhang School of Mathematical Sciences Peking University

In this paper, we solve Beck and Wayne's conjecture on the optimal enhanced dissipation rate for the 2-D linearized Navier-Stokes equations around the bar state called the Kolmogorov flow by developing the hypocoerciv... 详细信息

关键词： Navier-Stokes equations Kolmogorov flow enhanced dissipation hypocoercivity method

DIMPLE IMPERFECTION SENSITIVITY OF SUBMARINE PIPELINES UNDER COMBINED EXTERNAL PRESSURE AND AXIAL LOAD

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China Ocean Engineering 1989年第4期4卷 499-507页

作者： Huang, Yuying Yue, dongyi Huazhong Univ of Science and Technology China

Based on the Karman-Donnell shell equations, a two-timing perturbation technique together with Fourier series expansion is used to solve an imperfection sensitivity problem of submarine pipelines with dimple shaped initial deflection under external pressure combined with axial load. The relationship between limit load and initial postbuckling coefficient as well as imperfection parameter is obtained. It shows that these submarine pipelines are imperfection-sensitive to a dimple shaped imperfection over a large range of a geometrical parameter and that the effect of the dimple shaped imperfection on limit load depends only upon its linear buckling mode component of the corresponding Fourier series expansion.

关键词： Mathematical Techniques Sensitivity Analysis

Combined Effect of Aluminum Content and Layer Structure on the Oxidation Performance of Ti_(1-x)Al_xN Based Coatings

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Journal of Materials Science & Technology 2014年第8期30卷 803-807页

作者： Jihua Peng dongyi Su Chengxi Wang School of Materials Science and Engineering South China University of Technology Guangzhou Jingtai Technology Co. Ltd.

TiN,Ti1-xAIxN single layer coatings and TiN/Ti1-xAIxN multilayer coatings were deposited on SKH51 tool steel substrate by arc ion *** coatings were annealed in air to study the effect of aluminum and film structure on the oxidation *** surface morphology and structure were characterized by scanning electron microscopy and X-ray *** element distribution on the cross section was analyzed by electron probe *** is found that the oxidation resistance of these Ti1-xAlxN based coatings is mainly attributed to aluminum content in *** comparison with the Ti1-xAlxN single layer coating,the TiN layer inserting into the Ti1-xAlxN in a multilayer coating increases the tendency of Ti diffusion toward the surface and forms a Ti-enriched top surface oxide layer,thus degrades the oxidation *** far as the oxidation resistance is concerned in this study,Ti0.33Al0.67N single layer coating performs the best among all *** kinetic of oxidation behavior of all coatings presents two definite *** is a slow oxidation growth which conforms to parabolic law,and the other presents severe mass gain with oxidation *** annealing time for severe oxidation initiation is responsible to Fe2O3formation in the oxide scale.

关键词： TixAl1-xN films Vacuum arc ion plating Oxidation resistance Microstructures

Sediment dynamic responses of coastal salt marsh to typhoon “KAEMI” in Quanzhou Bay,Fujian Province,China

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Chinese Science Bulletin 2009年第1期54卷 120-130页

作者： WANG AiJun GAO Shu CHEN Jian LI dongyi Ministry of Education Key Laboratory for Coast and Island Development Nanjing University Nanjing 210093 China Open Laboratory for Coast & Ocean Environmental Geology Third Institute of Oceanography State Oceanic Administration Xiamen 361005 China

In order to understand the mechanisms of coastal protection by salt marshes during typhoon events,in situ measurements of water level,tidal current speed and direction,and suspended sediment concen-tration (SSC) were carried out using Electromagnetic Current Meter (EMCM,AEM HR),miniature pres-sure sensor (MkV/D) and Seapoint Turbidity Meter (STM) sensor on a tidal flat in Quanzhou Bay,during the period when the typhoon "KAEMI" was passing through the region. The analysis of the data ob-tained shows that the near-bed current speed within the Spartina alterniflora marsh was generally be-low 5 cm s-1,which was apparently smaller than on the adjacent bare flat (i.e. 5―30 cm s-1). The change in the near-bed current speed in response to the typhoon event was not significant within the S. al-terniflora marsh,but the current direction was influenced by the typhoon. The effect of the typhoon on the SSC was highly significant,with the SSC reaching 13 to 19 times the values on the bare flat or within the marsh under fair weather conditions; the near-bed SSC within the marsh was higher than on the bare flat,after the typhoon landed. The near-bed suspended sediment fluxes within the marsh and on the bare flat during the typhoon event were both enhanced,i.e.,4 times larger than under fair weather conditions. During the ebb,the bottom shear stress on the bare flat exceeded the critical shear stress for sediment motion for most of the ebb duration of the tide and,therefore,the bed sediment was eroding,with the erosion flux after the typhoon landed being around 2 to 3 times the value associated with fair weather conditions. In contrast,within the S. alterniflora marsh,the bottom shear stress was mostly lower than the critical shear stress for sediment motion,or lower than the critical shear stress for the maintenance of suspension; hence,the marsh surface was dominated by settling processes,with a settling flux during the typhoon being 3 to 6 times compared with the fair weather sit

关键词：碱湿地沉淀物动态过程台风福建

GlobalWell-Posedness for the 2-DMHD Equations with Magnetic Diffusion

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Communications in Mathematical Research 2020年第4期36卷 377-389页

作者： dongyi Wei Zhifei Zhang School of Mathematical Sciences Peking University100871BeijingP.R.China.

In this paper,we consider the 2-D MHD equations with magnetic resistivity but without dissipation on the *** prove that if the initial data is small in H4(T2),then the 2-D MHD equations are globally *** our knowledge,... 详细信息

关键词： MHD equations globally well-posedness.

Efficient generation of complex vectorial optical fields with metasurfaces

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Light(Science & Applications) 2021年第4期10卷 681-694页

作者： dongyi Wang Feifei Liu Tong Liu Shulin Sun Qiong He Lei Zhou State Key Laboratory of Surface Physics Key Laboratory of Micro and Nano Photonic Structures(Ministry of Education)and Department of PhysicsFudan UniversityShanghaiChina Shanghai Engineering Research Centre of Ultra-Precision Optical Manufaauring Green Photonics and Department of Optical Science and EngineeringFudan UniversityShanghaiChina Academy for Engineering and Technology Fudan UniversityShanghaiChina Collabo rative Innovation Centre of Advanced Microstructures NanjingChina

Vectorial optical fields(VOFs)exhibiting arbitrarily designed wavefronts and polarization distributions are highly desired in ***,current methods to generate them either require complicated setups or exhibit limited functionalities,which is unfavorable for integration-optics ***,we propose a generic approach to efficiently generate arbitrary VOFs based on metasurfaces exhibiting full-motrix yet inhomogeneous Jones-matrix *** illustrate our strategy with analytical calculations on a model system and an experimental demonstration of a meta-device that can simultaneously deflect light and manipulate its *** on these benchmark results,we next experimentally demonstrate the generation of a far-field VOF exhibiting both a vortex wavefront and an inhomogeneous polarization ***,we design/fabricate a meta-device and experimentally demonstrate that it can generate a complex near-field VOF-a cylindrically polarized surface plasmon wave possessing orbital angular momentum-with an efficiency of-34%.Our results establish an efficient and ultracompact platform for generating arbitrary predesigned VOFs in both the near-and far-fields,which may find many applications in optical manipulation and communications.

关键词： arbitrary inhomogeneous generating

ADVANCES IN SURGICAL TREATMENT OF ACOUSTIC NEUROMA

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Journal of Otology 2012年第2期7卷 62-66页

作者： HAN dongyi CAI Chaochan Department of Otolaryngology Head and Neck Surgery PLA General Hospital

Acoustic Neuroma (AN) arises from the eighth cranial nerve. It primarily involves the vestibular branch of the nerve and is therefore also called vestibular schwannoma(VS). To the date, diagnosis and surgical treatment of AN have advanced significantly. Along with advances in audiology and imaging technologies, cases of diagnosed AN have been increasing, making it a common

关键词： Figure IAC ADVANCES IN SURGICAL TREATMENT OF ACOUSTIC NEUROMA than

Asymptotic decay for the Chern-Simons-Higgs equations

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Science China Mathematics 2024年

作者： dongyi Wei Shiwu Yang School of Mathematical Sciences Peking University Beijing International Center for Mathematical Research Peking University

In this paper, we study the long time asymptotic behaviors for solutions to the Chern-Simons-Higgs equations with a pure power defocusing nonlinearity. We obtain quantitative inverse polynomial time decay for the potential energy for all data with finite conformal energy. Consequently, the solution decays in time in the pointwise sense for all power. We also show that the solution decays as quickly as linear waves for sufficiently large powers. Key ingredients for the proof include the vector field method, conformal compactification, and the geometric bilinear trace theorem for null hypersurfaces developed by Klainerman and Rodnianski(2006).

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