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Feedback control of wave segments in an excitable medium

Chinese Physics B 2013年第5期22卷 187-190页

作者：吴宁杰高洪俊应和平 Jiangsu Key Laboratory for Numerical Simulation of Large Scale Complex Systems School of Mathematical SciencesNanjing Normal University Institute of Modern Physics and Department of Physics Zhejiang University

Depending on the excitability of the medium, a propagating wave segment will either contract or expand to fill the medium with spiral waves. This paper aims to introduce a simple mechanism of feedback control to stabilize such an expansion or contraction. To do this, we lay out a feedback control system in a block diagram and reduce it into a bare, universal formula. Analytical and experimental findings are compared through a series of numerical simulations of the Barkley model.

关键词： feedback control wave segments excitable medium

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Dynamical energy equipartition of the Toda model with additional on-site potentials

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Chinese Physics B 2017年第10期26卷 107-111页

作者：张振俊唐春梅康静童培庆 College of Science Hohai University School of Physics and Technology Nanjing Normal University Jiangsu Provincial Key Laboratory for Numerical Simulation of Large Scale Complex Systems Nanjing Normal University

We study the dynamical energy equipartition properties in the integrable Toda model with additional uniform or disordered on-site energies by extensive numerical simulations. The total energy is initially equidistributed among some of the lowest frequency linear modes. For the Toda model with uniform on-site potentials, the energy spectrum keeps its profile nearly unchanged in a relatively short time scale. On a much longer time scale, the energies of tail modes increase slowly with time. Energy equipartition is far away from being attached in our studied time scale. For the Toda model with disordered on-site potentials, the energy transfers continuously to the high frequency modes and eventually towards energy equipartition. We further perform a systematic study of the equipartition time teq depending on the energy density ε and the nonlinear parameter α in the thermodynamic limit for the Toda model with disordered on-site potentials. We find teq∝ （1/ε）^a（1/α）^b, where b≈ 2a. The values of a and b are increased when increasing the strengths of disordered on-site potentials or decreasing the number of initially excited modes.

关键词： energy transport behaviors Toda model uniform or disordered on-site potentials

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Dynamical quantum phase transition in XY chains with the Dzyaloshinskii-Moriya and XZY-YZX three-site interactions

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Chinese Physics B 2022年第6期31卷 260-266页

作者： Kaiyuan Cao Ming Zhong Peiqing Tong Department of Physics and Institute of Theoretical Physics Nanjing Normal UniversityNanjing 210023China Jiangsu Key Laboratory for Numerical Simulation of Large Scale Complex Systems Nanjing Normal UniversityNanjing 210023China

We study the dynamical quantum phase transitions(DQPTs)in the XY chains with the Dzyaloshinskii-Moriya interaction and the XZY-YZX type of three-site interaction after a sudden *** the models can be mapped to the spinless free fermion models by the Jordan-Wigner and Bogoliubov transformations with the form■where the quasiparticle excitation spectraεkmay be smaller than 0 for some k and are asymmetrical■It is found that the factors of Loschmidt echo equal 1 for some k corresponding to the quasiparticle excitation spectra of the pre-quench Hamiltonian satisfyingε_(k)·ε_(-k)<0,when the quench is from the gapless *** considering the quench from different ground states,we obtain the conditions for the occurrence of DQPTs for the general XY chains with gapless phase,and find that the DQPTs may not occur in the quench across the quantum phase transitions regardless of whether the quench is from the gapless phase to gapped phase or from the gapped phase to gapless *** is different from the DQPTs in the case of quench from the gapped phase to gapped phase,in which the DQPTs will always ***,we analyze the different reasons for the absence of DQPTs in the quench from the gapless phase and the gapped *** conclusion can also be extended to the general quantum spin chains.

关键词： dynamical quantum phase transition gapless phase asymmetry excitation spectra

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A New Analytical Solution for Tide-Induced Groundwater Fluctuations in An Unconfined Aquifer with A Sloping Beach

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China Ocean Engineering 2011年第3期25卷 479-494页

作者：孔俊宋志尧辛沛沈城吉 College of Harbor Coastal and Offshore Engineering Hohai University Key Laboratory of Virtual Geographic Environment under Ministry of Education and Jiangsu Key Laboratory for Numerical Simulation of Large-Scale Complex SystemNanjing Normal University National Centre for Groundwater Research and Training The University of Queensland

Deriving analytical solutions for tide-induced groundwater fluctuations in unconfined aquifers confronts two problems：（1） As the Boussinesq equation itself contains nonlinear terms, the ＂secular term＂ would be generated in derivation, thus making perturbation solution unable to be deduced to higher order; （2） for aquifers with sloping beaches, the perturbation parameter in existing analytical solution integrating the beach slope and hydrogeological property would be sometimes larger than 1. So the application of perturbation solutions is relatively limited. Furthermore, as the beach slope decreases, the error of analytical solution would gradually increase. Given that water table over-height would increase the aquifer thickness and speed up wave propagation, this paper integrates over-height into the perturbation parameter and adjusts boundary conditions to settle the problem of ＂secular term＂ and to derive a new high-order analytical solution for nonlinear Boussinesq equation in terms of sloping beaches. Results show that the new analytical solution is more reasonable, and the analytical accuracy is obviously improved in comparison with the existing analytical solution for a gentle slope. The new analytical solution provides a theoretical basis for analyzing the propagation characteristics （e.g., wave length and over-height variation） of tide-induced groundwater wave in unconfined aquifers, particularly those with sloping beaches.

关键词： tide groundwater analytical solution over-height perturbation method

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Supertetragonal BaZrS_(3):A promising perovskite sulphide with giant ferroelectricity and low band gap

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Science China(Physics,Mechanics & Astronomy) 2024年第8期67卷 126-133页

作者： Menglu Li Sa Zhang Chenhan Liu Xiaotao Zu Liang Qiao Haiyan Xiao School of Physics University of Electronic Science and Technology of ChinaChengdu 611731China College of Mathematics and Physics Chengdu University of TechnologyChengdu 610059China Micro-and Nano-scale Thermal Measurement and Thermal Management Laboratory Ministry of Education Key Laboratory of Numerical Simulation of Large-Scale Complex SystemsSchool of Energy and Mechanical EngineeringNanjing Normal UniversityNanjing 210023China

Over the past century,ferroelectricity has offered exciting opportunities for fundamental research and device ***,most of the discovered excellent ferroelectrics are oxide materials with large band gaps,limiting their potential for optoelectronics *** using first-principles calculations we identify a new narrow-gap ferroelectric beyond oxides,i.e.,ferroelectric perovskite sulphide BaZrS_(3).Under large compressive strains,BaZrS_(3)can be stabilized into a unique supertetragonal phase with an extraordinary polarization of 67.16μC/cm^(2),which is even stronger than that of conventional oxide ***,the supertetragonal BaZrS_(3)exhibits a direct narrow band gap of 1.2 eV and excellent electronic *** on the chemical bonding analysis,we attribute the formation of supertetragonal phase to charge re-ordering in which theπbond overlap along the long〈Zr-S〉bond completely vanishes and the antibonding states of theσbond appear below the Fermi *** work provides a conceptual strategy for designing new ferroelectrics for electronic and photovoltaic applications.

关键词： supertetragonal phase perovskite sulphide ferroelectricity

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Semileptonic decays B/Bs→(D^(?),D^(?)s)lνl in the PQCD approach with the lattice QCD input

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Chinese Physics C 2020年第5期44卷 8-21页

作者： Xue-Qing Hu Su-Ping Jin Zhen-Jun Xiao Department of Physics and Institute of Theoretical Physics Nanjing Normal UniversityNanjing 210023China Jiangsu Key Laboratory for Numerical Simulation of Large Scale Complex Systems Nanjing Normal UniversityNanjing 210023China

We study the semileptonic B/Bs→(D^(?),D^(?)s)lνl decays in the framework of the Standard Model(SM),by employing the perturbative QCD(PQCD)factorization formalism combined with the lattice QCD input for the relevant transition form *** calculate the branching ratios B(B(s)→D^(?)(s)lνl)with l=(e,μ,τ),the ratios of the branching fractions R(D^(?))and R(D^(?)s),and the physical observables Pτ(D^(?)(s)),FL(D?(s))and AFB(τ).The“PQCD+Lattice”predictions for B(B→D^(?)lνl)and R(D^(?))agree with the available experimental measurements within *** the ratios R(Ds)and R(D^?s),the"PQCD+Lattice"predictions agree with the other *** Pτ(D^?)and FL(D^?),our theoretical predictions agree with the measured values within *** theoretical predictions of the semileptonic B/Bs decays considered could be tested in the near future by the LHCb and Belle II experiments.

关键词： semileptonic decays form factor PQCD Bs meson

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Semileptonic decays B_c■(η_c, J/ψ)l■_l in the “PQCD+Lattice” approach

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Chinese Physics C 2020年第2期44卷 51-61页

We study the semileptonic decaysBc-→(ηc,J/ψ)l-■lusing the PQCD factorization approach with the newly defined distribution amplitudes of the B c meson and a new kind of parametrization for extrapolating the form factors which takes into account the recent lattice QCD *** find the following main results:(a)the PQCD predictions of the branching ratios of theBc→(ηc,J/ψ)l■decays are smaller by about 5%-16%when the lattice results are taken into account in the extrapolation of the relevant form factors;(b)the PQCD predictions of the ratio Rηc,RJ/ψand of the longitudinal polarization PτareRηc=0.34±0.01,RJ/ψ=0.28±0.01,Pτ(ηc)=0.37±0.01and Pτ(J/ψ)=-0.55±0.01;and(c)after including the lattice results,the theoretical predictions slightly change:Rηc=0.31±0.01,RJ/ψ=0.27±0.01,Pτ(ηc)=0.36±0.01andPτ(J/ψ)=-0.53±*** theoretical predictions of RJ/ψagree with the measurements within the *** other predictions could be tested by the LHCb experiment in the near future.

关键词： semileptonic Bc decays PQCD approach lattice QCD results ratio of branching ratios longitudinal polarization

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Comparison and Modification: TVD Schemes for Scalar Transport on An Unstructured Grid

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China Ocean Engineering 2016年第4期30卷 615-626页

作者：张卓宋志尧郭飞张东温永宁胡迪 Key Lab of Virtual Geographic Environment under Ministry of Education Nanjing Normal University Jiangsu Center for Collaborative Innovation in Geographical Information Resource Development and Application Nanjing Normal University Jiangsu Key Lab for Numerical Simulation of Large-Scale Complex System Nanjing Normal University

In most TVD schemes, the r-factors were proposed according to the cell-centered（CC） finite volume method（FVM） framework for the numerical approximation to the convective term. However, it is questionable whether those r-factors would be appropriate and effective for the vertex-centered（VC） FVM. In the paper, we collected five kinds of r-factor formulae and found out that only three of those, respectively by Bruner（1996）, Darwish and Moukalled（2003） and Cassuli and Zanolli（2005） can be formally extended to a context of the VC FVM. numerical tests indicate that the TVD schemes and r-factors, after being extended and introduced to a context of the VC FVM, maintained their similar characteristics as in a context of the CC FVM. However, when the gradient-based r-factors and the SUPERBEE scheme were applied simultaneously, non-physical oscillations near the sharp step would appear. In the transient case, the oscillations were weaker in a context of the VC FVM than those in a context of the CC FVM, while the effect was reversed in the steady case. To eliminate disadvantages in the gradient-based r-factor formula, a new modification method by limiting values on the virtual node, namely Фu in the paper, was validated by the tests to effectively dissipate spurious oscillations.

关键词： TVD scheme unstructured grid vertex-centered FVM flux limiter, r-factor

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On Compressible Smooth Viscous Fluids in Slowly Expanding Balls

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Analysis in Theory and Applications 2019年第1期35卷 28-65页

作者： Huicheng Yin Lin Zhang School of Mathematical Sciences Jiangsu Provincial Key Laboratory for Numerical Simulation of Large Scale Complex Systems Nanjing Normal University

In[17]and[19,20],the global existence and large time behaviors of smooth compressible fluids(including inviscid gases of Euler equations,viscous gases of Navier-Stokes equations,and rarified gases of Boltzmann equation,respectively)have been established in an infinitely expanding ball with a constant expansion *** paper concerns with the viscous fluids in a slowly expanding *** involved analy-sis on the density function and the weighted energy estimates,we show that the fluid in the slowly expanding ball smoothly tends to a vacuum state and there is no appearance of vacuum in any part of the expansive *** present result is a meaningful supplement to the one in[19].

关键词： Compressible Navier-Stokes equations slowly expanding ball weighted energy estimate global existence

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A Modification to Vertical Distribution of Tidal Flow Reynolds Stress in Shallow Sea

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China Ocean Engineering 2012年第3期26卷 431-442页

作者：倪志辉宋志尧张绪进吴立春易静 Key Laboratory of Hydraulic and Waterway Engineering of the Ministry of Education and National Engineering Research Center for Inland Waterway RegulationChongqing Jiaotong University Southwestern Research Institute of Water Transportation Engineering Chongqing Jiaotong University Key Lab of Virtual Geographic Environment under Ministry of Education and Jiangsu Key Lab for Numerical Simulation of Large-Scale Complex SystemNanjing Normal University Chongqing University of Education

Tidal flow is a periodic movement of unsteady and non-uniform, which has acceleration and deceleration process obviously, especially in coastal shallow waters. Many researches show that vertical distribution of tidal flow Reynolds stress deviated from linear distribution. The parabolic distribution of the tidal flow Reynolds stress was proposed by Song et al. （2009）. Although the model fills better with field observations and indoor experimental data, it has the lower truncated series expansion of tidal flow Reynolds stress, and the description of the distribution is not very comprehensive By introducing the motion equation of tidal flow and improving the parabolic distribution established by Song et al. （2009）, the cubic distribution of the tidal flow Reynolds stress is proposed. The cubic distribution is verified well by field data （Bowden and Fairbairn, 1952; Bowden et al., 1959; Rippeth et al., 2002） and experimental data （Anwar and Atkins, 1980）, is consistent with the numerical model results of Kuo et al. （1996）, and is compared with the parabolic distribution of the tidal flow Reynolds stress. It is shown that this cubic distribution is not only better than the parabolic distribution, but also can better reflect the basic features of Reynolds stress deviating from linear distribution downward with the tidal flow acceleration and upward with the tidal flow deceleration, for the foundation of further study on the velocity profile of tidal flow.

关键词： tidal flow Reynolds stress linear distribution parabolic distribution cubic distribution

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