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A hybrid phase field method for fluid-structure interactions in viscous fluids

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arXiv 2021年

作者： Hong, Qi Wang, Qi College of Science Nanjing University of Aeronautics and Astronautics Nanjing210016 China MIIT Nanjing211106 China Jiangsu Key Laboratory for Numerical Simulation of Large Scale Complex System Department of Mathematics University of South Carolina ColumbiaSC29208 United States

We present a novel computational modeling framework to numerically investigate fluid-structure interaction in viscous fluids using the phase field embedding method. Each rigid body or elastic structure immersed in the incompressible viscous fluid matrix, grossly referred to as the particle in this paper, is identified by a volume preserving phase field. The motion of the particle is driven by the fluid velocity in the matrix for passive particles or combined with its self-propelling velocity for active particles. The excluded volume effect between a pair of particles or between a particle and the boundary is modeled by a repulsive potential force. The drag exerted to the fluid by a particle is assumed proportional to its velocity. When the particle is rigid, its state is described by a zero velocity gradient tensor within the nonzero phase field that defines its profile and a constraining stress exists therein. While the particle is elastic, a linear constitutive equation for the elastic stress is provided within the particle domain. A hybrid, thermodynamically consistent hydrodynamic model valid in the entire computational domain is then derived for the fluid-particle ensemble using the generalized Onsager principle accounting for both rigid and elastic particles. Structure-preserving numerical algorithms are subsequently developed for the thermodynamically consistent model. numerical tests in 2D and 3D space are carried out to verify the rate of convergence and numerical examples are given to demonstrate the usefulness of the computational framework for simulating fluid-structure interactions for passive as well as self-propelling active particles in a viscous fluid matrix. Copyright © 2021, The Authors. All rights reserved.

关键词： Hydrodynamics

Evaluation method for information security capability of mobile phone user based on behavior ontology under unconscious condition

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Tongxin Xuebao/Journal on Communications 2016年 37卷 156-167页

作者： Mai, Cheng-Cheng Chen, Bo Zhou, Jia-Kun Yu, Ling School of Computer Science and Technology Nanjing Normal University Nanjing210023 China Jiangsu Provincial Key Laboratory for Numerical of Large Scale Complex System Nanjing210023 China

A security capacity assessment method based on security behavior ontology, was proposed to collect users' behavior data from their smartphones under unconscious condition to solve the problem of detecting mobile phone users' real existing insecure behaviors. A security behavior ontology was set up for formalizing the phone, message, network and App behavior data of mobile phone users and relevant rules were also set down for determining and associating insecure actions. Referring to the notion of attack graph, an insecure behavior detection algorithm was proposed based on behavior association graph for analyzing the paths of insecure behaviors dynamically. Furthermore, a competency model of information security capability assessment was presented for realizing the quantitative evaluation of information security capability of users. The experiment results prove the effectiveness of present competency model for insecure behavior path detection and security ability assessment. © 2016, Editorial Board of Journal on Communications. All right reserved.

关键词： Ontology

Directed momentum current induced by the PT-symmetric driving

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Physical Review E 2019年第4期99卷 042201-042201页

作者： Wen-Lei Zhao Jiaozi Wang Xiaohui Wang Peiqing Tong School of Science Jiangxi University of Science and Technology Ganzhou 341000 China Department of Modern Physics University of Science and Technology of China Hefei 230026 China School of Information Engineering Jiangxi University of Science and Technology Ganzhou 341000 China Department of Physics and Institute of Theoretical Physics Nanjing Normal University Nanjing 210023 China Jiangsu Provincial Key Laboratory for Numerical Simulation of Large Scale Complex Systems Nanjing Normal University Nanjing Jiangsu 210023 China

We investigate the directed momentum current in the quantum kicked rotor model with PT-symmetric deriving potential. For the quantum nonresonance case, the values of quasienergy become complex when the strength of the imaginary part of the kicking potential exceeds a threshold value, which demonstrates the appearance of the spontaneous PT symmetry breaking. In the vicinity of the transition point, the momentum current exhibits a staircase growth with time. Each platform of the momentum current corresponds to the mean momentum of some eigenstates of the Floquet operator whose imaginary parts of the quasienergy are significantly large. Above the transition point, the momentum current increases linearly with time. Interestingly, its acceleration rate exhibits a kind of “quantized” increment with the kicking strength. We propose a modified classical acceleration mode of the kicked rotor model to explain such an intriguing phenomenon. Our theoretical prediction is in good agreement with numerical results.

关键词： Coherent control Cold atoms & matter waves Light-matter interaction Wave chaos

Spontaneous PT-symmetry breaking in non-Hermitian Kitaev and extended Kitaev models

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Physical Review A 2015年第1期92卷 012116-012116页

作者： Xiaohui Wang Tingting Liu Ye Xiong Peiqing Tong Department of Physics and Institute of Theoretical Physics Nanjing Normal University Nanjing 210023 People's Republic of China Jiangsu Key Laboratory for Numerical Simulation of Large Scale Complex Systems Nanjing Normal University Nanjing 210023 People's Republic of China and Kavli Institute for Theoretical Physics China CAS Beijing 100190 People's Republic of China

The spontaneous parity-time (PT) symmetry breaking is discussed in non-Hermitian PT-symmetric Kitaev and extended Kitaev models whose Hermiticity is broken by the presence of two conjugated imaginary potentials ±iγ at two end sites. In the case of the non-Hermitian Kitaev model, a spontaneous PT-symmetry breaking transition (SPTBT) occurs at a certain γc in the topologically trivial phase (TTP) region, similar to that of the Su-Schrieffer-Heeger (SSH) model. However, unlike the SSH model, the system also undergoes such a transition in the topologically nontrivial phase (TNP) region. We study an extended Kitaev model by combining the superconducting pairing in the Kitaev model and the staggered hopping in the SSH model. This model contains three different topological phases: the TTP, the Kitaev-like TNP, and the SSH-like TNP. For the non-Hermitian extended Kitaev model, a SPTBT occurs in the Kitaev-like TNP region, as well as in part of the TTP and SSH-like TNP regions, whereas the PT symmetry is broken for an arbitrary nonzero γ in the rest of the TTP and SSH-like TNP regions. Therefore, we can conclude that there is no universal correlation between topological properties and the SPTBT.

关键词： TANTALUM compounds QUADRUPOLE moments ELECTRON-nucleus scattering HYPERFINE structure QUANTUM chromodynamics

Work done and irreversible entropy production in a suddenly quenched quantum spin chain with asymmetrical excitation spectra

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Physical Review E 2015年第3期91卷 032137-032137页

作者： Ming Zhong Peiqing Tong Department of Physics and Institute of Theoretical Physics Nanjing Normal University Nanjing 210023 People's Republic of China Jiangsu Key Laboratory for Numerical Simulation of Large Scale Complex Systems Nanjing Normal University Nanjing 210023 People's Republic of China and Kavli Institute for Theoretical Physics China CAS Beijing 100190 People's Republic of China

In this paper, we extend the studies on the emergent thermodynamics in a quenched quantum Ising chain (QIC) [R. Dorner, J. Goold, C. Cormick, M. Paternostro, and V. Vedral, Phys. Rev. Lett. 109, 160601 (2012)] to a more general quantum spin chain with asymmetrical excitation spectra. We verify that the Jarzynski and Tasaki-Crooks relations are still tenable in this system. As an example, we discuss the behaviors of the work done and irreversible entropy production induced by a sudden quenching in the anisotropic XY chain in a transverse field with the XZY-YZX type of three-site interactions. Different from the QIC, this system has the phase transitions not only between two gapped phases, but also between gapped (or gapless) and gapless phases at zero temperature. We discuss the effects of quantum phase transitions on the work done and irreversible entropy production at low temperature.

关键词： ISING model THERMODYNAMICS QUANTUM systems QUANTUM phase transitions LOW temperature physics

On semilinear Tricomi equations with critical exponents or in two space dimensions

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arXiv 2017年

作者： He, Daoyin Witt, Ingo Yin, Huicheng Department of Mathematics and IMS Nanjing University Nanjing210093 China Mathematical Institute University of Göttingen Bunsenstr. 3-5 GöttingenD-37073 Germany School of Mathematical Sciences Jiangsu Provincial Key Laboratory for Numerical Simulation of Large Scale Complex Systems Nanjing Normal University Nanjing210023 China

This paper is a complement of our recent works on the semilinear Tricomi equations in [8] and [9]. For the semilinear Tricomi equation ∂t2u−t∆u = |u|p with initial data (u(0, ·), ∂tu(0, ·)) = (u0, u1), where t ≥ 0, x ∈ Rn (n ≥ 3), p > 1, and ui ∈ C0∞(Rn) (i = 0, 1), we have shown in [8] and [9] that there exists a critical exponent pcrit(n) > 1 such that the solution u, in general, blows up in finite time when 1 crit(n), and there is a global small solution for p > pcrit(n). In the present paper, firstly, we prove that the solution of ∂t2u − t∆u = |u|p will generally blow up for the critical exponent p = pcrit(n) and n ≥ 2, secondly, we establish the global existence of small data solution to ∂t2u − t∆u = |u|p for p > pcrit(n) and n = 2. Thus, we have given a systematic study on the blowup or global existence of small data solution u to the equation ∂t2u − t∆u = |u|p for n ≥ 2.35L70, 35L65, 35L67 Copyright © 2017, The Authors. All rights reserved.

关键词：

The Schrödinger equation for general non-hermitian quantum system

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arXiv 2017年

作者： Xiong, Ye Tong, Peiqing Department of Physics and Institute of Theoretical Physics Nanjing Normal University Nanjing210023 China National Laboratory of Solid State Microstructures Nanjing University Nanjing210093 China Jiangsu Key Laboratory for Numerical Simulation of Large Scale Complex Systems Nanjing Normal University Nanjing210023 China

We derive a new time-dependent Schrödinger equation(TDSE) for quantum models with nonhermitian Hamiltonian. Within our theory, the TDSE is symmetric in the two Hilbert spaces spanned by the left and the right eigenstates, respectively. The physical quantities are also identical in these two spaces. Based on this TDSE, we show that exchanging two quasi-particles in a non-hermitian model can generate arbitrary geometric phase. The system can also violate the Lieb-Robinson bound in non-relativistic quantum mechanics so that an action in one place will immediately cause a change in the distance. We show that the above two surprising behaviors can also appear in anyonic model, which makes us propose that the non-hermitian single particle model may possess many common features with anyonic model. Copyright © 2017, The Authors. All rights reserved.

关键词： Quantum optics

Fully charm and bottom pentaquarks in a lattice-QCD inspired quark model

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Physical Review D 2022年第1期106卷 014005-014005页

作者： Gang Yang Jialun Ping Jorge Segovia Department of Physics Zhejiang Normal University Jinhua 321004 China Department of Physics and Jiangsu Key Laboratory for Numerical Simulation of Large Scale Complex Systems Nanjing Normal University Nanjing 210023 China Departamento de Sistemas Físicos Químicos y Naturales Universidad Pablo de Olavide E-41013 Sevilla Spain

The fully charm and bottom pentaquarks, i.e., ccccc¯ and bbbbb¯, with spin-parity quantum numbers JP=12−, 32−, and 52−, are investigated within a lattice-QCD inspired quark model, which has already successfully described the recently announced fully charm tetraquark candidate X(6900) and has also predicted several other fully heavy tetraquarks. A powerful computational technique, based on the Gaussian expansion method combined with a complex-scaling range approach, is employed to predict, and distinguish, bound, resonance, and scattering states of the mentioned five-body system. Both baryon-meson and diquark-diquark-antiquark configurations, along with all of their possible color channels are comprehensively considered. Narrow resonances are obtained in each spin-parity channel for the fully charm and bottom systems. Moreover, most of them seem to be compact multiquarks whose wave functions are dominated by either hidden-color baryon-meson or diquark-diquark-antiquark structure or by the coupling between them.

关键词： Quark model Strong interaction

Supplementary Variable Method for Developing Structure-Preserving numerical Approximations to Thermodynamically Consistent Partial Differential Equations

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arXiv 2020年

作者： Gong, Yuezheng Hong, Qi Wang, Qi College of Science Nanjing University of Aeronautics and Astronautics Nanjing210016 China Beijing Computational Science Research Center Beijing100193 China Jiangsu Key Laboratory for Numerical Simulation of Large Scale Complex Systems Department of Mathematics University of South Carolina ColumbiaSC29208 United States

We present a new temporal discretization paradigm for developing energy-production-rate preserving numerical approximations to thermodynamically consistent partial differential equation systems, called the supplementary variable method. The central idea behind it is to introduce a supplementary variable to the thermodynamically consistent model to make the over-determined equation system, consisting of the thermodynamically consistent PDE system, the energy definition and the energy dissipation equation, structurally stable. The supplementary variable allows one to retain the consistency between the energy dissipation equation and the PDE system after the temporal discretization. We illustrate the method using a dissipative gradient flow model. Among virtually infinite many possibilities, we present two ways to add the supplementary variable in the gradient flow model to develop energy-dissipation-rate preserving algorithms. Spatial discretizations are carried out using the pseudo-spectral method. We then compare the two new schemes with the energy stable SAV scheme and the fully implicit Crank-Nicolson scheme. The results favor the new schemes in the overall performance. This new numerical paradigm can be applied to any thermodynamically consistent models. Copyright © 2020, The Authors. All rights reserved.

关键词： Partial differential equations