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Angular momentum of radiation from ultrarelativistic charge 超相对论电荷辐射的角动量
Pub Date : 2024-08-18 DOI: arxiv-2408.13272
Vladimir Epp, Ulyana Guselnikova, Julia Janz
The angular momentum of radiation from an arbitrarily moving relativisticcharge is studied. The angular momentum is presented as the sum of the angularmomentum relative to the point where the charge is located at a retarded momentof time and the angular momentum relative to an arbitrary stationary center. Inparticular, the instantaneous center of curvature of the trajectory isconsidered as such a center. Explicit expressions for the angular distributionof these components of angular momentum fluxes are obtained and studied. It isshown that the angular momentum of the field relative to the position of thecharge is determined only by the properties of the electromagnetic radiationfield, and the angular momentum relative to an arbitrarily distant point is thevector product of the displacement of this point and the force corresponding toradiation pressure. It is shown that in the ultrarelativistic limit, thecanonical angular momentum of the radiation coincides with the angular momentumfollowing from the symmetrized energy-momentum tensor of the electromagneticfield.
研究了任意运动的相对论电荷的辐射角动量。角动量是相对于电荷所在点在延时时刻的角动量与相对于任意静止中心的角动量之和。特别是,轨迹的瞬时曲率中心被视为这样一个中心。我们获得并研究了角动量通量的这些分量的角分布的明确表达式。结果表明,场相对于电荷位置的角动量仅由电磁辐射场的性质决定,而相对于任意遥远点的角动量是该点的位移与辐射压力相应的力的矢量乘积。研究表明,在超相对论极限,辐射的典型角动量与电磁场对称能动张量的角动量相吻合。
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引用次数: 0
Unusual Properties of Adiabatic Invariance in a Billiard Model Related to the Adiabatic Piston Problem 与绝热活塞问题有关的台球模型中绝热不变性的不寻常特性
Pub Date : 2024-08-17 DOI: arxiv-2409.07458
Joshua Skinner, Anatoly Neishtadt
We consider the motion of two massive particles along a straight line. Alighter particle bounces back and forth between a heavier particle and astationary wall, with all collisions being ideally elastic. It is known that ifthe lighter particle moves much faster than the heavier one, and the kineticenergies of the particles are of the same order, then the product of the speedof the lighter particle and the distance between the heavier particle and thewall is an adiabatic invariant: its value remains approximately constant over along period. We show that the value of this adiabatic invariant, calculated atthe collisions of the lighter particle with the wall, is a constant of motion(i.e., {an exact adiabatic invariant}). On the other hand, the value of thisadiabatic invariant at the collisions between the particles slowly andmonotonically decays with each collision. The model we consider is a highly simplified version of the classicaladiabatic piston problem, where the lighter particle represents a gas particle,and the heavier particle represents the piston.
我们考虑两个大质量粒子沿直线运动。较轻的粒子在较重的粒子和静止壁之间来回弹跳,所有碰撞都是理想的弹性碰撞。众所周知,如果较轻粒子的运动速度比较重粒子的运动速度快得多,并且粒子的动能是同阶的,那么较轻粒子的速度与较重粒子和墙之间距离的乘积就是绝热不变量:它的值在沿周期内保持近似恒定。我们证明,在较轻粒子与壁碰撞时计算出的这个绝热不变量的值是一个运动常数(即{一个精确的绝热不变量})。另一方面,粒子碰撞时的绝热不变量值会随着每次碰撞缓慢地单调衰减。我们所考虑的模型是经典绝热活塞问题的高度简化版本,其中较轻的粒子代表气体粒子,较重的粒子代表活塞。
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引用次数: 0
Displacement Current in Classical and Quantum Systems 经典和量子系统中的位移电流
Pub Date : 2024-08-14 DOI: arxiv-2408.13268
David K. Ferry, Xavier Oriols, Robert Eisenberg
It is certain that electrical properties-whether slow (sec) or fast (nsec),even optical (fsec)-are described by Maxwell's equations, and there are termsthat depend on the rate of change of the electric and magnetic fields. Inparticular, Maxwell's equation for the curl of the magnetic field contains boththe steady current and a term depending upon the temporal derivative of theelectric displacement field. The latter is referred to as displacement current,and is generally believed to have been included originally by Maxwell himself,although there is evidence it was earlier considered by Kirchhoff. Maxwell'sequations and Kirchoff's circuit laws both are important over the wide range offrequencies with which electronics traditionally deals. And, displacementcurrent is an important contribution to these in both classical and quantummechanics. Here, the development of displacement current, its importance inboth classical and quantum mechanics, and some applications are provided toillustrate the fundamental role that it plays in the dynamics of a wide rangeof systems.
可以肯定的是,无论是慢速(秒)还是快速(毫秒),甚至是光速(毫秒),电特性都是由麦克斯韦方程描述的,其中有一个项取决于电场和磁场的变化率。特别是,麦克斯韦磁场卷曲方程既包含稳定电流,也包含一个取决于电场位移的时间导数的项。后者被称为位移电流,一般认为最初是由麦克斯韦本人加入的,但有证据表明基尔霍夫在更早的时候也考虑过这一问题。麦克斯韦定律和基尔霍夫电路定律在电子学传统处理的宽频率范围内都非常重要。而位移电流在经典力学和量子力学中都有重要贡献。本文介绍了位移电流的发展、其在经典力学和量子力学中的重要性以及一些应用,以说明位移电流在各种系统动力学中的基本作用。
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引用次数: 0
Shortcuts to adiabaticity across a separatrix 跨分离矩阵绝热的捷径
Pub Date : 2024-08-13 DOI: arxiv-2408.06916
Roi Holtzman, Oren Raz, Christopher Jarzynski
Shortcuts to adiabaticity are strategies for conserving adiabatic invariantsunder non-adiabatic (i.e. fast-driving) conditions. Here, we show how to extendclassical, Hamiltonian shortcuts to adiabaticity to allow the crossing of aphase-space separatrix -- a situation in which a corresponding adiabaticprotocol does not exist. Specifically, we show how to construct atime-dependent Hamiltonian that evolves one energy shell to another energyshell across a separatrix. Leveraging this method, we design an erasureprocedure whose energy cost and fidelity do not depend on the protocol'sduration.
绝热捷径是在非绝热(即快速驱动)条件下保持绝热不变性的策略。在这里,我们展示了如何扩展经典的哈密顿绝热捷径,以允许跨越相空间分离矩阵--在这种情况下,并不存在相应的绝热协议。具体来说,我们展示了如何构建与时间相关的哈密顿,使一个能量壳跨越分离矩阵演化为另一个能量壳。利用这种方法,我们设计了一种擦除程序,其能量成本和保真度不依赖于协议的持续时间。
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引用次数: 0
Topological dynamics of continuum lattice structures 连续晶格结构的拓扑动力学
Pub Date : 2024-08-13 DOI: arxiv-2408.06898
Yimeng Sun, Jiacheng Xing, Li-Hua Shao, Jianxiang Wang
Continuum lattice structures which consist of joined elastic beams subject toflexural deformations are ubiquitous in nature and engineering. Here, first, wereveal the topological dynamics of continuous beam structures by rigorouslyproving the existence of infinitely many topological edge states within thebandgaps. Then, we obtain the analytical expressions for the topological phasesof bulk bands, and propose a topological index related to the Zak phase thatdetermines the existence of the edge states. The theoretical approach isdirectly applicable to general continuum lattice structures. We demonstrate thetopological edge states of bridge-like frames, plates, and continuous beams onelastic foundations and springs, and the topological corner states of kagomeframes. The continuum lattice structures serve as excellent platforms forexploring various kinds of topological phases and demonstrating thetopologically protected states at multifrequencies, and their topologicaldynamics has significant implications in safety assessment, structural healthmonitoring, and energy harvesting.
连续晶格结构由承受柔性变形的连接弹性梁组成,在自然界和工程中无处不在。在这里,我们首先通过严格证明带隙内存在无限多拓扑边缘态,揭示了连续梁结构的拓扑动力学。然后,我们得到了体带拓扑相的解析表达式,并提出了一种与扎克相相关的拓扑指数,它决定了边缘态的存在。这种理论方法直接适用于一般的连续晶格结构。我们展示了桥式框架、板、弹性地基和弹簧上的连续梁的拓扑边缘态,以及卡戈米框架的拓扑角态。连续体晶格结构是探索各种拓扑相和展示多频率拓扑保护状态的绝佳平台,其拓扑动力学在安全评估、结构健康监测和能量收集方面具有重要意义。
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引用次数: 0
Non-linearity and chaos in the kicked top 踢顶的非线性和混乱
Pub Date : 2024-08-11 DOI: arxiv-2408.05869
Amit Anand, Robert B. Mann, Shohini Ghose
Classical chaos arises from the inherent non-linearity of dynamical systems.However, quantum maps are linear; therefore, the definition of chaos is notstraightforward. To address this, we study a quantum system that exhibitschaotic behavior in its classical limit: the kicked top model, whose classicaldynamics are governed by Hamilton's equations on phase space, whereas itsquantum dynamics are described by the Schr"odinger equation in Hilbert space.We explore the critical degree of non-linearity signifying the onset of chaosin the kicked top by modifying the original Hamiltonian so that thenon-linearity is parametrized by a quantity $p$. We find two distinct behaviorsof the modified kicked top depending on the value of $p$. Chaos intensifies as$p$ varies within the range of $1leq p leq 2$, whereas it diminishes for $p >2$, eventually transitioning to a purely regular oscillating system as $p$tends to infinity. We also comment on the complicated phase space structure fornon-chaotic dynamics. Our investigation sheds light on the relationship betweennon-linearity and chaos in classical systems, offering insights into theirdynamic behavior.
经典混沌产生于动力学系统固有的非线性。然而,量子映射是线性的;因此,混沌的定义并不直接。为了解决这个问题,我们研究了一个在经典极限中表现出混沌行为的量子系统:踢顶模型,其经典动力学受相空间上的汉密尔顿方程支配,而其量子动力学则由希尔伯特空间上的施dinger方程描述。我们发现修改后的踢顶有两种截然不同的行为,这取决于 $p$ 的值。当$p$在$1leq p leq2$范围内变化时,混沌会加剧;而当$p>2$时,混沌会减弱。我们还评论了非混沌动力学的复杂相空间结构。我们的研究揭示了经典系统中非线性与混沌之间的关系,为其动力学行为提供了启示。
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引用次数: 0
Acoustic Pancharatnam-Berry Geometric Phase Induced by Transverse Spin 横向自旋诱导的声学潘查拉特南-浆果几何相位
Pub Date : 2024-08-07 DOI: arxiv-2408.03513
Wanyue Xiao, Wenjian Kuang, Sibo Huang, Shanjun Liang, Din Ping Tsai, Shubo Wang
Common wisdom believes that the Pancharatnam-Berry (PB) geometric phase isabsent in acoustics due to the spin-0 nature of sound waves. We theoreticallyand experimentally demonstrate that the PB phase can emerge in surface soundwaves (SSWs) carrying transverse spin. The phase differs for the SSWspropagating in opposite directions due to spin-momentum locking. We furtherrealize acoustic PB metasurfaces for nearly arbitrary wavefront manipulation.Our work provides the missing piece of acoustic geometric phases, offering newinsights into the fundamental properties of sound waves and opening a newavenue for sound manipulation based on the PB phase.
一般认为,由于声波的自旋-0 特性,声学中不存在 Pancharatnam-Berry (PB) 几何相位。我们通过理论和实验证明,在携带横向自旋的表面声波(SSW)中可以出现 PB 相位。由于自旋-动量锁定,在相反方向传播的 SSW 中,相位是不同的。我们的工作为声学几何相位提供了缺失的部分,为声波的基本特性提供了新的见解,并为基于 PB 相位的声音操纵开辟了新的途径。
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引用次数: 0
Notes on the planar triangles in Minkowski spacetime 关于闵科夫斯基时空中平面三角形的说明
Pub Date : 2024-08-07 DOI: arxiv-2408.03898
Yan Cao
The geometry of 2D Minkowski spacetime $mathbb{R}^{1,1}$ (or Minkowskiplane) is similar but fundamentally different from the more familiar Euclideanplane geometry. This note gives an elementary discussion on some basicproperties of a triangle on the Minkowski plane. In particular, we show thatthe theorem of Feuerbach also holds and a use of the incenter/excenters ispointed out.
二维闵科夫斯基时空$mathbb{R}^{1,1}$(或闵科夫斯基平面)的几何与我们更熟悉的欧几里得平面几何相似,但又有本质区别。本论文将对闵科夫斯基平面上三角形的一些基本性质进行基本讨论。特别是,我们证明费尔巴哈定理也成立,并指出了入心/出心的用法。
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引用次数: 0
Careful finite element simulations of cold rolling with accurate through-thickness resolution and prediction of residual stress 以精确的厚度分辨率和残余应力预测对冷轧进行细致的有限元模拟
Pub Date : 2024-08-06 DOI: arxiv-2408.03242
Francis Flanagan, Alison O'Connor, Mozhdeh Erfanian, Omer Music, Edward James Brambley, Doireann O'Kiely
In this paper, we carefully develop a finite element (FE) model that givesaccurate through-thickness predictions of stress and strain distributionsduring the steady-state cold rolling process. These through-thicknesspredictions unveil an oscillatory pattern that is shown to have importantconsequences for residual stress in the rolled sheet. We believe this is thefirst time that through-thickness FE results have been accurately validated bycomparison to non-FE results, in this case by comparison to a recent analyticalmodel of through-thickness variation in cold rolling. While we use here theABAQUS commercially available FE software, our observations are relevant to allFE simulations of cold rolling. Care is taken by considering both convergencein number of elements through thickness, convergence to a steady state, and theavoidance of other numerical artefacts such as shear locking and hourglassing.We find that previous FE models of cold rolling are usually woefullyunder-resolved through-thickness; e.g. using 10 elements through-thickness,while we require 60 here for convergence. Convergence of roll force and rolltorque, used in previous studies to validate models, are shown to be poorindicators of through-thickness convergence. We also show that thethrough-thickness oscillatory pattern may have important consequences forpredicting curvature during asymmetric rolling.
在本文中,我们精心开发了一个有限元(FE)模型,该模型能准确预测稳态冷轧过程中的通厚应力和应变分布。这些贯通厚度预测揭示了一种振荡模式,该模式对轧制板材中的残余应力具有重要影响。我们相信,这是首次通过与非有限元结果进行比较来精确验证贯通厚度有限元结果,在这种情况下,是通过与最新的冷轧贯通厚度变化分析模型进行比较来验证。虽然我们在这里使用的是 ABAQUS 市售有限元分析软件,但我们的观察结果与所有冷轧有限元模拟都相关。我们仔细考虑了各厚度元素数量的收敛性、向稳定状态的收敛性,以及避免剪切锁定和沙漏等其他数值误差。我们发现,以前的冷轧有限元模型通常对各厚度的分辨率严重不足;例如,使用 10 个各厚度元素,而我们这里需要 60 个元素才能收敛。以往研究中用于验证模型的轧辊力和轧辊扭矩的收敛性,被证明是通厚收敛性的不良指标。我们还表明,厚度振荡模式可能对预测非对称轧制过程中的曲率具有重要影响。
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引用次数: 0
Deciphering Complexity: Machine Learning Insights into Chaotic Dynamical Systems 解密复杂性:机器学习对混沌动力系统的启示
Pub Date : 2024-08-04 DOI: arxiv-2408.02005
Lazare Osmanov
We introduce new machine-learning techniques for analyzing chaotic dynamicalsystems. The primary objectives of the study include the development of a newand simple method for calculating the Lyapunov exponent using only twotrajectory data points unlike traditional methods that require an averagingprocedure, the exploration of phase transition graphs from regular periodic tochaotic dynamics to identify "almost integrable" trajectories where conservedquantities deviate from whole numbers, and the identification of "integrableregions" within chaotic trajectories. These methods are applied and tested ontwo dynamical systems: "Two objects moving on a rod" and the "Henon-Heiles"systems.
我们为分析混沌动力学系统引入了新的机器学习技术。研究的主要目标包括:开发一种新的简单方法,仅使用两个轨迹数据点计算李亚普诺夫指数,而不像传统方法需要一个平均过程;探索从规则周期动力学到混沌动力学的相变图,以识别守恒量偏离整数的 "几乎可积分 "轨迹;以及识别混沌轨迹中的 "可积分区域"。这些方法在两个动力学系统中得到了应用和检验:"两个物体在一根杆上运动 "和 "Henon-Heiles "系统。
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引用次数: 0
期刊
arXiv - PHYS - Classical Physics
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