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Lifespan of Solutions to MHD Boundary Layer Equations with Analytic Perturbation of General Shear Flow

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Acta Mathematicae Applicatae Sinica 2019年第1期35卷 209-229页

作者： feng xie Tong YANG School of Mathematical Sciences and LSC-MOE Shanghai Jiao Tong University Department of Mathematics City University of Hong Kong School of Mathematical Sciences Shanghai Jiao Tong University

In this paper, we consider the lifespan of solution to the MHD boundary layer system as an analytic perturbation of general shear flow. By using the cancellation mechanism in the system observed in [12], the lifespan of solution is shown to have a lower bound in the order of ε^(-2-) if the strength of the perturbation is of the order of ε. Since there is no restriction on the strength of the shear flow and the lifespan estimate is larger than the one obtained for the classical Prandtl system in this setting, it reveals the stabilizing effect of the magnetic field on the electrically conducting fluid near the boundary.

关键词： MHD boundary layer analytic perturbation lifespan estimate shear flow

Remarks on Sharp Interface Limit for an Incompressible Navier-Stokes and Allen-Cahn Coupled System

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Chinese Annals of Mathematics,Series B 2023年第5期44卷 663-686页

作者： Song JIANG Xiangxiang SU feng xie Institute of Applied Physics and Computational Mathematics Beijing 100088China School of Mathematical Sciences Shanghai Jiao Tong UniversityShanghai 200240China School of Mathematical Sciences CMA-ShanghaiShanghai Jiao Tong UniversityShanghai 200240China

The authors are concerned with the sharp interface limit for an incompressible Navier-Stokes and Allen-Cahn coupled system in this *** the thickness of the diffuse interfacial zone,which is parameterized by ε,goes to zero,they prove that a solution of the incompressible Navier-Stokes and Allen-Cahn coupled system converges to a solution of a sharp interface model in the L^(∞)(L^(2))∩L^(2)(H^(1))sense on a uniform time interval independent of the small parameterε.The proof consists of two parts:One is the construction of a suitable approximate solution and another is the estimate of the error functions in Sobolev *** the careful energy estimates,a spectral estimate of the linearized operator for the incompressible Navier-Stokes and Allen-Cahn coupled system around the approximate solution is essentially used to derive the uniform estimates of the error *** convergence of the velocity is well expected due to the fact that the layer of the velocity across the diffuse interfacial zone is relatively weak.

关键词： Sharp interface limit Incompressible Navier-Stokes equations AllenCahn equation Spectral estimate Energy estimates

Experimental study on detonation parameters and cellular structures of fuel cloud

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Acta Mechanica Sinica 2012年第2期28卷 438-443页

作者： Li-feng xie Bin Li Yu-Lei Zhang School of Chemical Engineering Nanjing University of Science and Technology210094 NanjingChina

In this paper, detonation parameters of fuel cloud, such as propylene oxide （PO）, isopropyl nitrate （IPN）, hex- ane, 90# oil and decane were measured in a self-designed and constructed vertical shock tube. Results show that the deto- nation pressure and velocity of PO increase to a peak value and then decrease smoothly with increasing equivalence ra- tio. Several nitrate sensitizers were added into PO to make fuel mixtures, and test results indicated that the additives can efficiently enhance detonation velocity and pressure of fuel cloud and one type of additive n-propyl nitrate （NPN） played the best in the improvement. The critical initiation energy that directly initiated detonation of all the test liquid fuel clouds showed a U-shape curve relationship with equiva- lence ratios. The optimum concentration lies on the rich-fuel side （;b 〉 1）. The critical initiation energy is closely related to molecular structure and volatility of fuels. IPN and PO have similar critical values while that of alkanes are larger. Detonation cell sizes of PO were respectively investigated at 25;C, 35;C and 50;C with smoked foil technique. The cell width shows a U-shape curve relationship with equivalence ratios at all temperatures. The minimal cell width also lies on the rich-fuel side （;b 〉 1）. The cell width of PO vapor is slightly larger than that of PO cloud. Therefore, the deto- nation reaction of PO at normal temperature is controlled by gas phase reaction.

关键词： Cloud detonation Detonation velocity Deto- nation pressure - Critical initiation energy Cell size

Numerical Simulations of Liquid-Solid Flows in A Vertical Pipe by MPS-DEM Coupling Method

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China Ocean Engineering 2022年第4期36卷 542-552页

作者： xie feng-ze MENG Qing-jie WAN De-cheng Computational Marine Hydrodynamics Lab(CMHL) School of Naval ArchitectureOcean and Civil EngineeringShanghai Jiao Tong UniversityShanghai 200240China Wuhan Second Ship Design and Research Institute Wuhan 430205China

In the process of deep-sea mining,the liquid-solid flows in the vertical transportation pipeline are very *** the present work,an in-house solver MPSDEM-SJTU based on the improved MPS and DEM is developed for the simulation of hydraulic ***,three examples including the multilayer cylinder collapse,the Poiseuille flow and two-phase dam-break are used to validate the precision of the DEM model,the pipe flow model and MPS-DEM coupling model,***,the hydraulic conveying with coarse particles in a vertical pipe is *** solid particle distribution is presented and investigated in ***,the coupling method is successfully applied for the simulation of the liquid-solid flows in a vertical pipe with rotating blades,which shows the stability of the solver under rotating boundary *** fully Lagrangian model is expected to be a new approach for analyzing hydraulic conveying.

关键词： liquid-solid flows MPS DEM vertical pipe rotating boundary conditions

CFD simulations of three-dimensional violent sloshing flows in tanks based on MPS and GPU

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Journal of Hydrodynamics 2020年第4期32卷 672-683页

作者： feng-ze xie Wei-wen Zhao De-cheng Wan Computational Marine Hydrodynamics Lab(CMHL) School of Naval ArchitectureOcean and Civil EngineeringState Key Laboratory of Ocean EngineeringShanghai Jiao Tong UniversityShanghai 200240China

For violent sloshing,the flow field becomes complicated and 3-D effect is *** addition to the excitation direction,the wave can also propagate perpendicular to the excitation *** to the superposition of waves from different directions,the impact pressure imposed on the wall of the tank may *** this paper,our in-house solver MPSGPU-SJTU based on moving particle semi-implicit(MPS)method coupled with GPU techniques is employed for the liquid sloshing simulation,to study the factors leading to the 3-D ***,a series of sloshing simulations are carried out to validate the reliability of present ***,the sensitivity of 3-D effect against some parameters,such as excitation frequency,dimensions of the tank and filling ratio,is checked through numerical *** histories of pressure obtained by 2-D and 3-D simulations are compared to judge the occurrence of 3-D *** concludes that effects of those parameters are all significant.

关键词： Liquid sloshing 3-D effect sensitive parameters moving particle semi-implicit(MPS)method MPSGPU-SJTU solver

TST: Threshold Based Similarity Transitivity Method in Collaborative Filtering with Cloud Computing

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Tsinghua Science and Technology 2013年第3期18卷 318-327页

作者： feng xie Zhen Chen Hongfeng Xu Xiwei feng Qi Hou Department of Automation Research Institute of Information Technology and Tsinghua National Laboratory for Information Science and Technology (TNList) Tsinghua University Research Institute of Information Technology and Tsinghua National Laboratory for Information Science and Technology (TNList) Tsinghua University Department of Computer Science and Technologies and Tsinghua National Laboratory for Information Science and Technology (TNList) Tsinghua University Department of Electronic Engineering and Tsinghua National Laboratory for Information Science and Technology (TNList) Tsinghua University

Collaborative filtering solves information overload problem by presenting personalized content to individual users based on their interests, which has been extensively applied in real-world recommender systems. As a class of simple but efficient collaborative filtering method, similarity based approaches make predictions by finding users with similar taste or items that have been similarly chosen. However, as the number of users or items grows rapidly, the traditional approach is suffering from the data sparsity problem. Inaccurate similarities derived from the sparse user-item associations would generate the inaccurate neighborhood for each user or item. Consequently, its poor recommendation drives us to propose a Threshold based Similarity Transitivity （TST） method in this paper. TST firstly filters out those inaccurate similarities by setting an intersection threshold and then replaces them with the transitivity similarity. Besides, the TST method is designed to be scalable with MapReduce framework based on cloud computing platform. We evaluate our algorithm on the public data set MovieLens and a real-world data set from AppChina （an Android application market） with several well-known metrics including precision, recall, coverage, and popularity. The experimental results demonstrate that TST copes well with the tradeoff between quality and quantity of similarity by setting an appropriate threshold. Moreover, we can experimentally find the optimal threshold which will be smaller as the data set becomes sparser. The experimental results also show that TST significantly outperforms the traditional approach even when the data becomes sparser.

关键词： cloud computing recommender systems big data collaborative filtering data mining similarity transitivity machine learning mapReduce android applications

Preparation and Microstructure of Glass-ceramics and Ceramic Composite Materials

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Journal of Wuhan University of Technology(Materials Science) 2008年第4期23卷 562-565页

作者： HE feng xie Junlin HAN Da School of Materials Science and Engineering Wuhan University of Technology Wuhan 430070 China

The technology and microstructure of glass-ceramics and ceramic composite materials were studied. A suitable ceramic body was chosen on the basis of the sintering temperature of CaO-Al2O3-SiO2 system glass-ceramics. According to the expansion coefficient of the ceramic body, that of CaO-Al2O3-SiO2 system glass-ceramics was adjusted, fl-wollastonite was found present as the major crystalline phase in glass- ceramic. The CaO-Al2O3-SiO2 system glass-ceramic layer and ceramic body could be sintered together by adjusting the sintering period. The compositions of glass-ceramic layer and ceramic body diffuse mutually at 1 100 ℃, resulting in an interface between them. To achieve good sintered properties of glass-ceramics and the chosen ceramic body, at least a four-hour sintering time is used.

关键词： CaO-Al2O3-SiO2 system glass-ceramic ceramic body

A note on the ill-posedness of shear flow for the MHD boundary layer equations

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Science China Mathematics 2018年第11期61卷 2065-2078页

作者： Cheng-Jie Liu feng xie Tong Yang Institute of Natural Sciences Shanghai Jiao Tong University School of Mathematical Sciences and Key Laboratory of Scientific and Engineering Computing(Ministry of Education) Shanghai Jiao Tong University Department of Mathematics City University of Hong Kong

For the two-dimensional Magnetohydrodynamics(MHD)boundary layer system,it has been shown that the non-degenerate tangential magnetic field leads to the well-posedness in Sobolev spaces and high Reynolds number limits without any monotonicity condition on the velocity field in our previous *** paper aims to show that sufficient degeneracy in the tangential magnetic field at a non-degenerate critical point of the tangential velocity field of shear flow indeed yields instability as for the classical Prandtl equations without magnetic field studied by G′erard-Varet and Dormy(2010).This partially shows the necessity of the non-degeneracy in the tangential magnetic field for the stability of the boundary layer of MHD in 2D at least in Sobolev spaces.

关键词： MHD boundary layer Prandtl equations shear flows ill-posedness Sobolev spaces

Phosphorus-doped Ni–Co sulfides connected by carbon nanotubes for flexible hybrid supercapacitor

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Frontiers of Chemical Science and Engineering 2023年第5期17卷 491-503页

作者： Shengwang Su Li Sun feng xie Jialong Qian Yihe Zhang Engineering Research Center of Ministry of Education for Geological Carbon Storage and Low Carbon Utilization of Resources Beijing Key Laboratory of Materials Utilization of Nonmetallic Minerals and Solid WastesNational Laboratory of Mineral MaterialsSchool of Materials Science and TechnologyChina University of GeosciencesBeijing 100083China

As promising electrode materials for supercapacitors,nickel-cobalt bimetallic sulfides render the advantages of abundant redox reactions and inherently high ***,in general,unsatisfactory performance of low specific capacity,low rate capability,and fast capacity loss exist in Ni–Co sulfide ***,we rationally regulate phosphorus-doped nickel–cobalt sulfides(P-NCS)to enhance the electrochemical performance by gas–solid ***,carbon nanotubes(CNTs)as conductive additives are added to improve the cycle stability and conductivity and form the composite P-NCS/C/*** to density functional theory,more electrons near the Fermi surface of P-NCS are demonstrated notionally than those of simple *** results manifest that P-NCS/C/CNT exhibits superior electrochemical performance,e.g.,high specific capacity(932.0 C·g^(-1)at 1 A·g^(-1)),remarkable rate capability(capacity retention ratio of 69.1%at 20 A·g^(-1)),and lower charge transfer *** importantly,the flexible hybrid asymmetric supercapacitor is assembled using P-NCS/C/CNT and activated carbon,which renders an energy density of 34.875 W·h∙kg^(-1)at a power density of 375 W∙kg^(-1).These results show that as-prepared P-NCS/C/CNT demonstrates incredible possibility as a battery-type electrode for high-performance supercapacitors.

关键词： cobalt nickel sulfide phosphorus-doping hybrid supercapacitor carbon nanotube density functional theory