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Implicit-explicit Runge-Kutta methods for Landau-Lifshitz equation with arbitrary damping 具有任意阻尼的 Landau-Lifshitz 方程的隐含-显式 Runge-Kutta 方法
IF 1 4区 数学 Q2 MATHEMATICS, APPLIED Pub Date : 2024-07-15 DOI: 10.4310/cms.2024.v22.n5.a9
Yan Gui, Cheng Wang, Jingrun Chen
Magnetization dynamics in ferromagnetic materials is modeled by the Landau-Lifshitz (LL) equation, a nonlinear system of partial differential equations. Among the numerical approaches, semi-implicit schemes are widely used in the micromagnetics simulation, due to a nice compromise between accuracy and efficiency. At each time step, only a linear system needs to be solved and a projection is then applied to preserve the length of magnetization. However, this linear system contains variable coefficients and a non-symmetric structure, and thus an efficient linear solver is highly desired. If the damping parameter becomes large, it has been realized that efficient solvers are only available to a linear system with constant, symmetric, and positive definite (SPD) structure. In this work, based on the implicit-explicit Runge-Kutta (IMEX-RK) time discretization, we introduce an artificial damping term, which is treated implicitly. The remaining terms are treated explicitly. This strategy leads to a semi-implicit scheme with the following properties: (1) only a few linear systems with constant and SPD structure needs to be solved at each time step; (2) it works for the LL equation with arbitrary damping parameter; (3) high-order accuracy can be obtained with high-order IMEX-RK time discretization. Numerically, second-order and third-order IMEX-RK methods are designed in both the 1-D and 3-D domains. A comparison with the backward differentiation formula scheme is undertaken, in terms of accuracy and efficiency. The robustness of both numerical methods is tested on the first benchmark problem from National Institute of Standards and Technology. The linearized stability estimate and optimal rate convergence analysis are provided for an alternate IMEX-RK2 numerical scheme as well.
铁磁材料中的磁化动态是由 Landau-Lifshitz (LL) 方程建模的,这是一个非线性偏微分方程系统。在各种数值方法中,半隐式方案因其在精度和效率之间的良好折衷而被广泛应用于微磁学模拟。在每个时间步长上,只需要求解一个线性系统,然后应用投影来保持磁化长度。然而,该线性系统包含可变系数和非对称结构,因此非常需要高效的线性求解器。如果阻尼参数变大,人们已经意识到,只有具有恒定、对称和正定(SPD)结构的线性系统才有高效的求解器。在这项工作中,基于隐式-显式 Runge-Kutta (IMEX-RK) 时间离散化,我们引入了一个人工阻尼项,并对其进行了隐式处理。其余项则采用显式处理。这种策略导致半隐式方案具有以下特性:(1) 每个时间步只需求解几个具有常数和 SPD 结构的线性系统;(2) 它适用于具有任意阻尼参数的 LL 方程;(3) 通过高阶 IMEX-RK 时间离散化可以获得高阶精度。在数值上,设计了一维和三维领域的二阶和三阶 IMEX-RK 方法。在精度和效率方面,与后向微分公式方案进行了比较。在美国国家标准与技术研究院的第一个基准问题上,对两种数值方法的稳健性进行了测试。此外,还为另一种 IMEX-RK2 数值方案提供了线性化稳定性估计和最佳速率收敛分析。
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引用次数: 0
Chemotactic reaction enhancement in one dimension 一维的趋化反应增强
IF 1 4区 数学 Q2 MATHEMATICS, APPLIED Pub Date : 2024-07-15 DOI: 10.4310/cms.2024.v22.n5.a5
Yishu Gong, Alexander Kiselev
Chemotaxis, which involves the directed movement of cells in response to a chemical gradient, plays a crucial role in a broad variety of biological processes. Examples include bacterial motion, the development of single-cell or multicellular organisms, and immune responses. Chemotaxis directs bacteria’s movement to find food (e.g., glucose) by swimming toward the highest concentration of food molecules. In multicellular organisms, chemotaxis is critical to early development (e.g., movement of sperm towards the egg during fertilization). Chemotaxis also helps mobilize phagocytic and immune cells at sites of infection, tissue injury, and thus facilitates immune reactions. In this paper, we study a PDE system that describes chemotactic processes in one dimension, which may correspond to a thin channel, the setting relevant in many applications: for example, spermatozoa progression to the ovum inside a Fallopian tube or immune response in a blood vessel. Our objective is to obtain qualitatively precise estimates on how chemotaxis improves reaction efficiency, when compared to purely diffusive situation. The techniques we use to achieve this goal include a variety of comparison principles and analysis of mass transport for a class of Fokker–Planck operators.
趋化作用是指细胞在化学梯度作用下的定向运动,在多种生物过程中发挥着至关重要的作用。例如,细菌运动、单细胞或多细胞生物体的发育以及免疫反应。趋化作用引导细菌游向食物分子浓度最高的地方寻找食物(如葡萄糖)。在多细胞生物体中,趋化性对早期发育至关重要(例如,受精过程中精子向卵子移动)。趋化还有助于在感染和组织损伤部位调动吞噬细胞和免疫细胞,从而促进免疫反应。在本文中,我们研究了一个描述一维趋化过程的 PDE 系统,该一维趋化过程可能相当于一个细通道,这在许多应用中都是相关的:例如,精子在输卵管内向卵子移动或血管中的免疫反应。我们的目标是对趋化如何提高反应效率(与纯扩散情况相比)进行定性精确估算。为实现这一目标,我们采用的技术包括各种比较原理以及对一类福克-普朗克算子的质量传输进行分析。
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引用次数: 0
Differentiable Hartman-Grobman Theorem via modulus of continuity: A sharp result on linearization in general Banach space 通过连续性模数的可微哈特曼-格罗布曼定理一般巴拿赫空间线性化的尖锐结果
IF 1 4区 数学 Q2 MATHEMATICS, APPLIED Pub Date : 2024-07-15 DOI: 10.4310/cms.2024.v22.n5.a8
Zhicheng Tong, Yong Li
As is well known the classical Hartman–Grobman theorem states that a $C^1$ mapping can be $C^0$ linearized near its hyperbolic fixed point in $mathbb{R}^n$. However, it is quite nontrivial to guarantee the local homeomorphism to be differentiable. Recently, the regularity assumption on derivative of the mapping has been weakened to Hölder’s type, significantly improving the work of $C^infty$, but still unknown for only differentiable case. We will try to touch this question in this paper. Without Hölder’s type, we first consider the existence and regularity of weak-stable manifolds for homeomorphisms with contraction in a Banach space, and further study linearization of mappings near hyperbolic fixed points. More precisely, we propose an Integrability Condition for regularity on linearization which is proved to be sharp, and establish a differentiable Hartman–Grobman theorem via modulus of continuity in a general Banach space. Thus we provide an almost complete answer to the question mentioned above.
众所周知,经典的哈特曼-格罗布曼定理指出,$C^1$映射可以在$mathbb{R}^n$的双曲定点附近被$C^0$线性化。然而,要保证局部同构是可微分的并不容易。最近,关于映射导数的正则性假设被弱化为荷尔德类型,大大改进了 $C^infty$ 的工作,但对于仅可微分的情况仍是未知数。我们将在本文中尝试探讨这个问题。在不考虑荷尔德类型的情况下,我们首先考虑巴拿赫空间中同构收缩的弱稳定流形的存在性和正则性,并进一步研究双曲定点附近映射的线性化。更确切地说,我们提出了线性化正则性的积分性条件(Integrability Condition),并证明该条件是尖锐的,同时通过一般巴拿赫空间中的连续性模数建立了可微哈特曼-格罗布曼定理。因此,我们几乎完整地回答了上述问题。
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引用次数: 0
Representation theorem for multivariable totally symmetric functions 多变量完全对称函数的表示定理
IF 1 4区 数学 Q2 MATHEMATICS, APPLIED Pub Date : 2024-07-15 DOI: 10.4310/cms.2024.v22.n5.a2
Chongyao Chen, Ziang Chen, Jianfeng Lu
In this work, we establish a representation theorem for multivariable totally symmetric functions: a multisymmetric continuous function must be the composition of a continuous function and a set of generators of the multisymmetric polynomials. We then study the singularity and geometry of the generators, and show that the regularity may become worse after applying the decomposition.
在这项工作中,我们建立了一个多变量完全对称函数的表示定理:一个多对称连续函数必须是一个连续函数和一组多对称多项式的生成器的组合。然后,我们研究了生成器的奇异性和几何性,并证明了应用分解后正则性可能会变差。
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引用次数: 0
Non-uniqueness of transonic shock solutions to Euler–Poisson system with varying background charges 背景电荷变化的欧拉-泊松系统跨音速冲击解的非唯一性
IF 1 4区 数学 Q2 MATHEMATICS, APPLIED Pub Date : 2024-03-04 DOI: 10.4310/cms.2024.v22.n3.a7
Ben Duan, Haoran Zheng
The Euler–Poisson equations with varying background charges in finitely long flat nozzles are investigated, for which two and only two transonic shock solutions are constructed. In href{https://dx.doi.org/10.4310/CMS.2012.v10.n2.a1}{[textrm{T. Luo and Z.P. Xin, Commun. Math. Sci., 10:419–462, 2012}]}, Luo and Xin established the wellposedness of steady Euler–Poisson equations for the constant background charge. Motivated by their pioneering work and combined with the special physical character of semiconductor devices, we propose the transonic shock problem in which the density of the background charge is a piecewise constant function and its discontinuity is determined only by shock fronts. The existence and non-uniqueness of transonic shock solutions are obtained via the method of shock matching.
研究了有限长平喷嘴中背景电荷变化的欧拉-泊松方程,构建了两个且仅有两个跨音速冲击解。在 href{https://dx.doi.org/10.4310/CMS.2012.v10.n2.a1}{[textrm{T. Luo and Z.P. Xin, Commun. Math. Sci.在他们开创性工作的激励下,结合半导体器件的特殊物理特性,我们提出了跨音速冲击问题,其中背景电荷密度是一个片断恒定函数,其不连续性仅由冲击前沿决定。通过冲击匹配方法,我们得到了跨音速冲击解的存在性和非唯一性。
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引用次数: 0
Hydrodynamic traffic flow models including random accidents: A kinetic derivation 包括随机事故在内的水动力交通流模型:动力学推导
IF 1 4区 数学 Q2 MATHEMATICS, APPLIED Pub Date : 2024-03-04 DOI: 10.4310/cms.2024.v22.n3.a10
Felisia Angela Chiarello, Simone Göttlich, Thomas Schillinger, Andrea Tosin
We present a formal kinetic derivation of a second order macroscopic traffic model from a stochastic particle model. The macroscopic model is given by a system of hyperbolic partial differential equations (PDEs) with a discontinuous flux function, in which the traffic density and the headway are the averaged quantities. A numerical study illustrates the performance of the second order model compared to the particle approach. We also analyse numerically uncertain traffic accidents by considering statistical measures of the solution to the PDEs.
我们从随机粒子模型出发,对二阶宏观交通模型进行了正式的动力学推导。宏观模型由一个双曲偏微分方程(PDE)系统给出,该系统具有不连续的流量函数,其中交通密度和车速是平均量。数值研究说明了二阶模型与粒子法相比的性能。我们还通过考虑 PDEs 解的统计量,对不确定的交通事故进行了数值分析。
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引用次数: 0
Autonomous vehicles driving traffic: The Cauchy problem 自动驾驶汽车在交通中行驶:考奇问题
IF 1 4区 数学 Q2 MATHEMATICS, APPLIED Pub Date : 2024-03-04 DOI: 10.4310/cms.2024.v22.n3.a9
Mauro Garavello, Francesca Marcellini
This paper deals with the Cauchy problem for a PDE‑ODE model, where a system of two conservation laws, namely the Two-Phase macroscopic model proposed in [Rinaldo M. Colombo, Francesca Marcellini, and Michel Rascle, $href{https://doi.org/10.1137/090752468}{textrm{SIAM J. Appl. Math., 70(7):2652–2666, 2010}}$], is coupled with an ordinary differential equation describing the trajectory of an autonomous vehicle (AV), which aims to control the traffic flow. Under suitable assumptions, we prove a global-in-time existence result.
本文讨论了一个 PDE-ODE 模型的考奇问题,在该模型中,两个守恒定律系统,即[Rinaldo M. Colombo, Francesca Marcellini, and Michel Rascle, $href{https://doi.org/10.1137/090752468}{textrm{SIAM J. Appl.在合适的假设条件下,我们证明了全局时间内的存在性结果。
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引用次数: 0
Analysis and computation for the scattering problem of electromagnetic waves in chiral media 手性介质中电磁波散射问题的分析与计算
IF 1 4区 数学 Q2 MATHEMATICS, APPLIED Pub Date : 2024-03-04 DOI: 10.4310/cms.2024.v22.n3.a5
Gang Bao, Lei Zhang
This paper considers an obstacle scattering problem in a chiral medium under circularly polarized oblique plane wave incidence, which can be represented as a combination of a left-circularly polarized plane wave and a right-circularly polarized one. We apply a reduced model problem with coupled oblique derivative boundary conditions, describing the cross-coupling effect of electric and magnetic fields. A novel boundary integral equation is constructed by introducing single-layer potential operators and the corresponding normal and tangential derivative operators. The corresponding properties are obtained by splitting techniques to overcome the singularity of integral operators. A numerical method for solving the boundary integral equation is developed, whose convergence is proved. Numerical results are presented to show the performance of the proposed method.
本文考虑了在圆极化斜平面波入射下手性介质中的障碍物散射问题,该问题可表示为左圆极化平面波和右圆极化平面波的组合。我们应用了带有耦合斜导数边界条件的简化模型问题,描述了电场和磁场的交叉耦合效应。通过引入单层势算子以及相应的法向和切向导数算子,构建了一个新的边界积分方程。通过分割技术克服积分算子的奇异性,从而获得相应的性质。建立了求解边界积分方程的数值方法,并证明了该方法的收敛性。数值结果显示了所提方法的性能。
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引用次数: 0
Improved uniform error bounds of an exponential wave integrator method for the Klein–Gordon–Schrödinger equation with the small coupling constant 具有小耦合常数的克莱因-戈登-薛定谔方程指数波积分器方法的改进均匀误差边界
IF 1 4区 数学 Q2 MATHEMATICS, APPLIED Pub Date : 2024-03-04 DOI: 10.4310/cms.2024.v22.n3.a1
Jiyong Li
Recently, the long-time numerical simulation and error analysis of PDEs with weak nonlinearity (or small potentials) become an interesting topic. However, the existing results of long-time error analysis mostly focus on the single equations. In this paper, for the Klein–Gordon–Schrödinger equation (KGSE) with a small coupling constant $varepsilon in (0,1]$, we propose an exponential wave integrator Fourier pseudo-spectral (EWIFP) method by reformulating the KGSE into a coupled nonlinear Schrödinger system (CNLSS). Through careful and rigorous analysis, we establish improved error bounds for the numerical solution at $O(h^m + varepsilon tau^2)$ in the long-time domain up to $O(1/varepsilon)$ where $m$ is determined by the regularity conditions, h is the mesh size and τ is the time step, respectively. Compared with the existing results, our analysis shows the long-time errors of numerical solution for the KGSE. In error analysis, in addition to the classical tools such as energy method and cut-off technique, we also adopt the regularity compensation oscillation (RCO) technique which has been developed recently to analyze the accumulation of errors carefully. The numerical experiments support our error estimates and demonstrate the long-term stability of discrete mass and energy. To the best of our knowledge, there has not been any relevant long-time error analysis for the KGSE and any improved uniform error bounds for an exponential wave integrator. Our work is novel and provides a reference for analyzing the improved error bounds of the numerical methods for other coupled equations.
近来,弱非线性(或小势)PDE 的长时间数值模拟和误差分析成为一个有趣的课题。然而,现有的长时间误差分析结果大多集中在单方程上。本文针对具有小耦合常数 $varepsilon in (0,1]$ 的克莱因-哥顿-薛定谔方程(KGSE),提出了一种指数波积分器傅立叶伪谱(EWIFP)方法,将 KGSE 重构为耦合非线性薛定谔系统(CNLSS)。通过细致严谨的分析,我们建立了改进的数值解误差边界,在长时域中为$O(h^m + varepsilon tau^2)$,最高为$O(1/varepsilon)$,其中$m$由正则条件决定,h为网格大小,τ为时间步长。与现有结果相比,我们的分析表明了 KGSE 数值解的长期误差。在误差分析中,除了能量法和截断技术等经典工具外,我们还采用了近年来发展起来的正则补偿振荡(RCO)技术来仔细分析误差的累积。数值实验支持了我们的误差估计,并证明了离散质量和能量的长期稳定性。据我们所知,目前还没有针对 KGSE 的相关长期误差分析,也没有针对指数波积分器的改进均匀误差边界。我们的工作很新颖,为分析其他耦合方程数值方法的改进误差边界提供了参考。
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引用次数: 0
Global existence and asymptotic behavior of the full Euler system with damping and radiative effects in $mathbb{R}^3$ 在 $mathbb{R}^3$ 中具有阻尼和辐射效应的全欧拉系统的全局存在性和渐近行为
IF 1 4区 数学 Q2 MATHEMATICS, APPLIED Pub Date : 2024-03-04 DOI: 10.4310/cms.2024.v22.n3.a8
Shijin Deng, Wenjun Wang, Feng Xie, Xiongfeng Yang
In this paper, we study the global existence and the large-time behavior of solutions to the Cauchy problem of the full Euler system with damping and radiative effects around some constant equilibrium states. It is well-known that the solutions may blow up in finite time without the additional damping and radiative effects, and the global existence of the solutions obtained in this paper shows that these two effects together prevent the formation of the singularity when the initial perturbation is small. Combining the Green’s function method and energy estimates, we consider the pointwise structures of the solutions to obtain a precise description of the system. The construction of the Green’s function includes three steps: singularity removal, long wave-short wave decomposition and weighted energy estimate. Finally, we achieve the pointwise estimates of the solutions in the small perturbation framework by Duhamel’s principle, the pointwise structure of the Green’s function established for the linearized equations and bounded estimates for higher order derivatives of the solutions together.
本文研究了具有阻尼和辐射效应的全欧拉系统 Cauchy 问题解在某些恒定平衡态附近的全局存在性和大时间行为。众所周知,如果没有额外的阻尼和辐射效应,解可能会在有限时间内炸毁,而本文得到的解的全局存在性表明,当初始扰动较小时,这两种效应共同阻止了奇点的形成。结合格林函数方法和能量估计,我们考虑了解的点式结构,从而获得了系统的精确描述。格林函数的构建包括三个步骤:奇点消除、长波-短波分解和加权能量估计。最后,我们通过杜哈梅尔原理、为线性化方程建立的格林函数点式结构以及解的高阶导数有界估计,在小扰动框架下实现了解的点式估计。
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引用次数: 0
期刊
Communications in Mathematical Sciences
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