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Coalescence of pore columns by domain switching

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Acta Mechanica Sinica 2006年第3期22卷 207-216页

作者： Liming geng Wei Yang Department of Engineering Mechanics Tsinghua University Beijing 100084 China

The present paper studies the coalescence of pore columns in ferroelectric ceramics driven by back and forth domain switching under cyclic electric field. A finite element method that incorporates mass transfer capacity is formulated to simulate the evolution of point defects subjected to the kinetics of pore surface diffusion and domain wall migration. The merge of point defects provides a mechanism for the vacancy agglomeration that leads to the formation of large pores or microcracks.

关键词： Point defect Ferroelectrics Domain switch Coalescence Structural evolution Finite element

Super twisting controller for on-orbit servicing to non-cooperative target

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Chinese Journal of Aeronautics 2015年第1期28卷 285-293页

作者： Chen Binglong geng Yunhai Research Center of Satellite Technology Harbin Institute of Technology

A relative position and attitude coupled controller is proposed for rendezvous and docking between two docking ports located in different spacecraft. It is concerned with servicing to a tumbling non-cooperative target spacecraft in arbitrary orbit subjected to external *** considering both kinematic and dynamical coupled effects of relative rotation on relative translation, a coupled dynamic model is established to represent the relative motion of docking port on target spacecraft with respect to another on the service spacecraft. The spacecraft control is based on the second order sliding mode algorithm of super twisting（ST）. It is schemed to manipulate the relative position and attitude synchronously. A formal proof of the finite time convergence property of the closed-loop system is derived theoretically by the second method of Lyapunov. Numerical simulations with the designed ST controller are presented to validate the analytic analysis by contrast with the twisting control algorithm. Simulation results demonstrate that the proposed relative position and attitude integrated controller is characterized by high precision, strong robustness and high reliability.

关键词： spacecraft orbit cooperative attitude robustness kinematic sliding dynamical rotation concerned

Beam-based optimization of SwissFEL low-level RF system

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Nuclear Science and Techniques 2018年第9期29卷 171-178页

作者： Zhe-Qiao geng Paul Scherrer Institut(PSI) 5232 VilligenSwitzerland

Swiss FEL is a free electron laser(FEL) under commissioning at the Paul Scherrer Institut(PSI) in Switzerland. Digital low-level RF(LLRF) systems are used in Swiss FEL to control more than 30 RF stations with either standing wave cavities(e.g. RF gun) or travelling wave structures working at different frequencies. After conditioned to desired power levels, the RF stations need to be setup for beam operation and the LLRF parameters need to be optimized for maximizing the beam stability. Several beam-based algorithms were developed to facilitate the setup, calibration and optimization of the Swiss FEL RF stations for beam operation. The algorithms were implemented as automation procedures in the framework of Experimental Physics and Industrial Control System(EPICS) and were used in commissioning and daily operation of Swiss FEL. In this paper, the algorithms and the implementation will be introduced together with the test results during the commissioning of SwissFEL.

关键词： SwissFEL LLRF optimization Beam-based calibration

Effect of Thermal Cycles on the Thermal Expansion Behavior of T700 Carbon Fiber Bundles

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Chemical Research in Chinese Universities 2018年第3期34卷 451-456页

作者： geng Guohang MA Xiaofei geng Hongbin WU Yiyong School of Materials Science and Engineering Harbin Institute of Technology Harbin 150001 P. R. China CAST-Xi 'an Institute of Space Radio Technology Xi 'an 710100 P. R. China

The relationships between the coefficient of thermal expansion（CTE） of T700 carbon fiber bundles（CFBs） and the thermal cycles were investigated. The microstructure of T700 CFBs was analyzed with Raman spectra and XRD before and after the thermomechanical test. The results indicated that the T700 CFBs exhibited negative expansion in the direction of parallel fibers in the temperature range of-150-150 ℃ The thermal strain that occurred during the heating and the cooling thermal cycle had an unclosed curve that served as the loop. When the experimental load was the same, the position of strain loop tended to move upward, and the length of the specimen increased continuously with the thermal cycles increasing. The microstructural analysis suggested that the degree of structural order and the degree of orientation along the fiber axis were improved with the increase of thermal cycles. The change of microstructure parameters could be the primary cause of the negative CTE＇s variation within the T700 CFBs.

关键词： T700 carbon fiber bundle Thermal cycle Coefficient of thermal expansion Microstructural analysis

Recent development in SU（3） covariant baryon chiral perturbation theory

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Frontiers of physics 2013年第3期8卷 328-348页

作者： Li-Sheng geng School of Physics and Nuclear Energy Engineering Beihang University Beijing 100191 China International Research Center for Nuclei and Particles in the Cosmos Beihang University Beijing 100191 China

Baryon chiral perturbation theory （BChPT）, as an effective field theory of low-energy quantum chromodynamics （QCD）, has played and is still playing an important role in our understanding of non-perturbative strong-interaction phenomena. In the past two decades, inspired by the rapid progress in lattice QCD simulations and the new experimental campaign to study the strangeness sector of low-energy QCD, many efforts have been made to develop a fully covariant BChPT and to test its validity in all scenarios. These new endeavours have not only deepened our understanding of some long-standing problems, such as the power-counting-breaking problem and the convergence problem, but also resulted in theoretical tools that can be confidently applied to make robust predic- tions. Particularly, the manifestly covariant BChPT supplemented with the extended-on-mass-shell （EOMS） renormalization scheme has been shown to satisfy all analyticity and symmetry constraints and converge relatively faster compared to its non-relativistic and infrared counterparts. In this article, we provide a brief review of the fully covariant BChPT and its latest applications in the u, d, and s three-flavor sector.

关键词： chiral Lagrangians lattice QCD calculations baryon resonances hyperons

Optimal Control of Non-well-posed Heat Equations

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Acta Mathematica Sinica,English Series 2005年第5期21卷 1005-1014页

作者： geng Sheng WANG Department of Mathematics Huazhong Normal University Wuhan 430079 P. R. China

This work is concerned with Pontryagin＇s maximum principle of optimal control problems governed by some non-well-posed semilinear heat equations. A type of approach to the non-well-posed optimal control problem is gi... 详细信息

关键词： Optimal control Non-well-posed heat equation State constraint

Large m asymptotics for minimal partitions of the Dirichlet eigenvalue

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Science China Mathematics 2022年第1期65卷 1-8页

作者： Zhiyuan geng Fanghua Lin Courant Institute of Mathematical Sciences New York UniversityNew YorkNY 10012USA

In this paper,we study large m asymptotics of the l 1 minimal m-partition problem for the Dirichlet *** any smooth domainΩ⊂R^(n)such that|Ω|=1,we prove that the limit lim_(m→∞)l^(1)_(m)(Ω)=c 0 exists,and the constant c 0 is independent of the shape ofΩ.Here,l^(1)_(m)(Ω)denotes the minimal value of the normalized sum of the first Laplacian eigenvalues for any m-partition ofΩ.

关键词： Dirichlet eigenvalue l1 minimal partition problem large m asymptotics

Rarefaction Wave Interaction and Shock-Rarefaction Composite Wave Interaction for a Two-Dimensional Nonlinear Wave System

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Chinese Annals of Mathematics,Series B 2021年第1期42卷 135-150页

作者： geng LAI Sisi XIE Department of Mathematics Shanghai UniversityShanghai 200444China

In order to construct global solutions to two-dimensional(2 D for short)Riemann problems for nonlinear hyperbolic systems of conservation laws,it is important to study various types of wave *** paper deals with two types of wave interactions for a 2 D nonlinear wave system with a nonconvex equation of state:Rarefaction wave interaction and shock-rarefaction composite wave *** order to construct solutions to these wave interactions,the authors consider two types of Goursat problems,including standard Goursat problem and discontinuous Goursat problem,for a 2 D selfsimilar nonlinear wave *** classical solutions to these Goursat problems are obtained by the method of *** solutions constructed in the paper may be used as building blocks of solutions of 2 D Riemann problems.

关键词： Nonlinear wave system Rarefaction wave Shock-rarefaction composite wave Wave interaction Characteristic decomposition

Application of the Chemical-Looping Concept for Azoetrope Separation

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Engineering 2021年第1期7卷 84-93页

作者： Xin Gao Xueli geng School of Chemical Engineering and Technology Tianjin University&National Engineering Research Center of Distillation Technology&Collaborative Innovation Center of Chemical Science and Engineering(Tianjin)Tianjin 300350China

The need for the separation of azeotropic mixtures for the production of high-end chemicals and resource recovery has spurred significant research into the development of new separation methods in the chemical *** this paper,a green and sustainable method for azeotrope separation is proposed based on a chemical-looping concept with the help of reversible-reaction-assisted *** central concept in the chemical-looping separation(CLS)method is the selection of a reactant that can react with the azeotrope components and can also be recycled by the reverse reaction to close the loop and achieve cyclic azeotrope *** paper aims to provide an informative perspective on the fundamental theory and applications of the CLS method based on the separation principle,reactant selection,and case analysis,for example,the separation of alkenes,alkane,aromatics,and polyol *** summary,we provide guidance and references for chemical separation process intensification in product refining and separation from azeotropic systems for the development of a more sustainable chemical industry.

关键词： Chemical-looping Azeotropes Reactive distillation Reactants screening Process intensification