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Superradiant scattering of orbital angular momentum beams 轨道角动量光束的超辐射散射
Pub Date : 2018-09-21 DOI: 10.1103/PhysRevResearch.3.023242
Cisco Gooding, S. Weinfurtner, W. Unruh
We consider the wave-structure coupling between an orbital angular momentum beam and a rapidly rotating disk, and present a new configuration exhibiting the wave amplification effect known as rotational superradiance. While initially envisioned in terms of the scattering of an incident wave directed perpendicular to an object's rotation axis, we demonstrate in the context of acousto-mechanics that superradiant amplification can also occur with a vortex beam directed parallel to the rotation axis. We propose two different experimental routes: one must either work with rotations high enough that the tangential velocity at the outer edge of the disk exceeds the speed of sound, or use evanescent sound waves. We argue that the latter possibility is more promising, and provides the opportunity to probe a previously unexamined parameter regime in the acoustics of rotating porous media.
我们考虑了轨道角动量光束和快速旋转圆盘之间的波结构耦合,并提出了一种新的结构,表现出被称为旋转超辐射的波放大效应。虽然最初设想的是垂直于物体旋转轴的入射波的散射,但我们在声学力学的背景下证明,平行于旋转轴的涡旋光束也可以发生超辐射放大。我们提出了两种不同的实验路线:一种必须使用足够高的旋转,使圆盘外缘的切向速度超过声速,或者使用消失的声波。我们认为后一种可能性更有希望,并提供了探索旋转多孔介质声学中以前未检查的参数制度的机会。
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引用次数: 7
On Maxwell’s electrodynamics in two spatial dimensions 二维麦克斯韦电动力学
Pub Date : 2018-09-20 DOI: 10.1590/1806-9126-rbef-2019-0323
D. Boito, L. D. Andrade, G. D. Sousa, R. Gama, C. Y. London
We discuss the construction of Maxwellian electrodynamics in 2+1 dimensions and some of its applications. Special emphasis is given to the problem of the retarded potentials and radiation, where substantial differences with respect to the usual three-dimensional case arise. These stem from the general form of the solutions of the wave equation in two dimensions, which we discuss using the Green's function method. We believe the topics presented here could be stimulating additions to an advanced electrodynamics course at the undergraduate level.
讨论了2+1维麦克斯韦电动力学的构造及其一些应用。特别强调了迟滞势和辐射的问题,这与通常的三维情况有很大的不同。这些源于二维波动方程解的一般形式,我们用格林函数法对其进行了讨论。我们相信这里提出的主题可以刺激补充到本科水平的高级电动力学课程。
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引用次数: 18
Force and Hidden Momentum for Classical Microscopic Dipoles 经典微观偶极子的力和隐动量
Pub Date : 2018-08-01 DOI: 10.2528/PIERB18092007
A. Yaghjian
The concept of hidden momentum is reviewed and the first rigorous derivation from Maxwell's equations is provided for the electromagnetic force on electrically small perfect electric conductors of arbitrary shape in bandlimited but otherwise arbitrarily time-varying fields. It is proven for the Amperian magnetic dipoles of these perfect conductors that a "hidden-momentum" electromagnetic force exists that makes the force on these time varying Amperian magnetic dipoles equal to the force on magnetic-charge magnetic dipoles with the same time varying magnetic dipole moment in the same time varying externally applied fields. The exact Mie solution to the perfectly conducting sphere under plane-wave illumination is used to prove that the expressions for the total and hidden-momentum forces on the arbitrarily shaped electrically small perfect conductors correctly predict the forces on perfectly conducting spheres. Remarkably, it is found that the quadrupolar fields at the surface of the sphere are required to obtain the correct total force on the sphere even though the quadrupolar moments are negligible compared to the dipole moments as the electrical size of the sphere approaches zero.
本文回顾了隐动量的概念,并首次从麦克斯韦方程组中给出了在带限场和任意时变场中作用于任意形状的电小完美导体上的电磁力的严格推导。对于这些完美导体的安氏磁偶极子,证明了存在一种“隐动量”电磁力,使得作用在这些时变安氏磁偶极子上的力等于作用在具有相同时变磁偶极矩的具有相同时变磁偶极子的磁荷磁偶极子上的力。用平面波照射下完美导电球的精确Mie解证明了任意形状的电小完美导体上的总动量和隐藏动量的表达式正确地预测了完美导电球上的力。值得注意的是,我们发现球表面的四极场需要得到正确的球上的总力,即使四极矩与偶极矩相比可以忽略不计,因为球的电尺寸接近于零。
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引用次数: 4
Dielectric slab reflection/transmission as a self-consistent radiation phenomenon. 介质板反射/传输作为自洽辐射现象。
Pub Date : 2018-06-24 DOI: 10.2528/PIERB18062303
J. Grzesik
We revisit the electromagnetic problem of wave incidence upon a uniform, dissipative dielectric slab of finite thickness. While this problem is easily solved via interface field continuity, we treat it under the viewpoint of radiative self-consistency, with interior current sources gauged by ohmic/polarization comparisons against those of the exterior medium. Radiative self-consistency yields an integral equation over the slab field giving a fully constructive buildup of the reflected/transmitted contributions, without any need for implicit determination via boundary conditions. Solution steps lead to an exact cancellation of the interior field, and bring in still other contributions of a reference medium variety, required to balance the incoming excitation. Such balancing provides the linear conditions for slab field determination. This two-step solution provides evidence of Ewald-Oseen extinction, even though the analytic framework here differs from the proofs available. We solve the balancing equations by vector manipulation without determinants, and then offer a boundary value confirmation in the special case of perpendicular incidence. In an appendix, we allow the the upper/lower half spaces to differ, the upper serving as reference and remote launch site of the incoming excitation. Effective currents now exist both within the slab and throughout an entire half space, necessitating a provision for cross-talk between slab and the radiating half space. The appendix provides an accelerated presentation of these generalized features, but stops short of an explicit field solution by reason of algebraic inflation. All logical details are however displayed in plain view. The self-consistency program is far more elegant and physically far more satisfying than the prevailing method of scattered fields guessed as to their structure and then fixed by boundary conditions.
我们重新讨论了有限厚度的均匀耗散介质板上的电磁波入射问题。虽然这个问题很容易通过界面场连续性来解决,但我们从辐射自洽的角度来处理它,通过欧姆/极化比较来测量内部电流源与外部介质的电流源。辐射自一致性产生了平板场上的积分方程,给出了反射/透射贡献的完全建设性累积,无需通过边界条件进行隐式确定。解的步骤导致内部场的精确消除,并引入了平衡入射激励所需的参考介质的其他贡献。这种平衡为板坯场的确定提供了线性条件。这个两步解提供了Ewald-Oseen灭绝的证据,尽管这里的分析框架与现有的证明不同。我们用不带行列式的矢量处理方法求解了平衡方程,并给出了垂直入射特殊情况下的边值确定。在附录中,我们允许上下半部分空间不同,上半部分作为输入激励的参考和远程发射点。有效电流现在既存在于板内,也存在于整个半空间内,因此需要在板和辐射半空间之间提供串扰。附录提供了这些广义特征的加速介绍,但由于代数膨胀的原因,没有给出显式的域解。然而,所有逻辑细节都以普通视图显示。自洽程序远比目前流行的散射场的结构猜测方法更优雅,在物理上也更令人满意,然后由边界条件固定。
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引用次数: 3
Symmetry reduction of the three-body problem based on Euler angles 基于欧拉角的三体问题对称化简
Pub Date : 2018-04-12 DOI: 10.1063/1.4990550
M. Castellana
We consider the classical three-body problem with an arbitrary pair potential which depends on the inter-body distance. A general three-body configuration is set by three "radial" and three angular variables, which determine the shape and orientation, respectively, of a triangle with the three bodies located at the vertices. The radial variables are given by the distances between a reference body and the other two, and by the angle at the reference body between the other two. Such radial variables set the potential energy of the system, and they are reminiscent of the inter-body distance in the two-body problem. On the other hand, the angular variables are the Euler angles relative to a rigid rotation of the triangle, and they are analogous to the polar and azimuthal angle of the vector between the two bodies in the two-body problem. We show that the rotational symmetry allows us to obtain a closed set of eight Hamilton equations of motion, whose generalized coordinates are the thee radial variables and one additional angle, for which we provide the following geometrical interpretation. Given a reference body, we consider the plane through it which is orthogonal to the line between the reference and a second body. We show that the angular variable above is the angle between the plane projection of the angular-momentum vector, and the projection of the radius between the reference and the third body.
我们考虑具有任意对势的经典三体问题,它取决于体间距离。一般的三体构型是由三个“径向”和三个角度变量设置的,它们分别决定三角形的形状和方向,三个体位于顶点。径向变量由一个参考体与另外两个参考体之间的距离以及参考体与另外两个参考体之间的夹角给出。这些径向变量决定了系统的势能,它们使人联想到两体问题中的体间距离。另一方面,角变量是相对于三角形刚体旋转的欧拉角,它们类似于二体问题中两个物体之间矢量的极角和方位角。我们表明,旋转对称性允许我们获得一个封闭的八个汉密尔顿运动方程,其广义坐标是三个径向变量和一个额外的角度,我们提供以下几何解释。给定一个参考物体,我们考虑通过它的平面与参考物体与第二物体之间的直线正交。我们表明,上面的角变量是角动量矢量的平面投影与参考物体和第三个物体之间的半径投影之间的夹角。
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引用次数: 0
Synchronization of a double pendulum with moving pivots: a study of the spectrum 带运动轴的双摆的同步:光谱的研究
Pub Date : 2018-02-14 DOI: 10.22606/JAAM.2018.34001
F. Talamucci
The model we consider consists in a double pendulum set, where the pivot points are free to shift along a horizontal line. Moreover, the two pendula are coupled by means of a spring whose extremities connect two points of each pendulum, at a fixed distance from the corresponding pivot. The mathematical model is first written encompassing a large class of setting for the device (different sizes, different physical properties, ...). In order to carry on the problem of synchronization via analytical me-thods, we focus on the circumstance of identical pendula: in that case, some classical theorems concerning the zeroes of polynomial equations are used in order to locate the eigenvalues governing the process, so that the possibility of synchronization of the device can be better understood.
我们考虑的模型包含一个双摆集,其中枢轴点沿水平线自由移动。此外,两个钟摆是通过弹簧连接起来的,弹簧的末端连接每个钟摆的两个点,与相应的枢轴保持固定的距离。数学模型首先包含了设备的一大类设置(不同的尺寸、不同的物理性质等)。为了用解析方法进行同步问题的研究,我们将重点放在了相同摆的情况下,在这种情况下,我们使用了一些关于多项式方程零点的经典定理来确定控制过程的特征值,从而更好地理解装置同步的可能性。
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引用次数: 1
Radiation Forces and the Abraham-Minkowski Problem 辐射力与亚伯拉罕-闵可夫斯基问题
Pub Date : 2017-12-30 DOI: 10.1142/S0217732318300069
I. Brevik
Recent years have witnessed a number of beautiful experiments in radiation optics. Our purpose with this mini-review is to highlight some developments of radiation pressure physics in general, and thereafter to focus on the importance of the mentioned experiments in regard to the classic Abraham-Minkowski problem. That means, what is the "correct" expression for electromagnetic momentum density in continuous matter. In our opinion one sees relatively often that authors over-interpret the importance of their experimental findings with respect to the momentum problem. Most of these experiments are actually unable to discriminate between these energy-momentum tensors at all, since they can be easily described in terms of force expressions that are common for Abraham and Minkowski. Moreover, we emphasize the inherent ambiguity in applying formal conservation principles to the radiation field in a dielectric, the reason being that the electromagnetic field in matter is only a subsystem which has to be supplemented by the mechanical subsystem to be closed. Finally, we make some suggestions regarding the connection between macroscopic electrodynamics and the Casimir effect, suggesting that there is a limit for the magnitudes of cutoff parameters in QFT related to surface tension in ordinary hydromechanics.
近年来,人们在辐射光学方面做了许多漂亮的实验。我们这篇小综述的目的是强调辐射压力物理学的一些发展,然后集中讨论上述实验对于经典的亚伯拉罕-闵可夫斯基问题的重要性。这意味着,连续物质中电磁动量密度的“正确”表达式是什么?在我们看来,人们经常看到作者过度解释他们的实验结果对动量问题的重要性。这些实验中的大多数实际上根本无法区分这些能量动量张量,因为它们可以很容易地用亚伯拉罕和闵可夫斯基常用的力表达式来描述。此外,我们强调将形式守恒原理应用于电介质中的辐射场时固有的模糊性,原因是物质中的电磁场只是一个子系统,必须由机械子系统来补充才能关闭。最后,我们对宏观电动力学与卡西米尔效应之间的联系提出了一些建议,表明普通流体力学中与表面张力相关的QFT中截止参数的大小是有限制的。
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引用次数: 24
Demystifying the constancy of the Ermakov-Lewis invariant for a time dependent oscillator 解时变振荡器Ermakov-Lewis不变量的常数
Pub Date : 2017-12-20 DOI: 10.1142/S0217732318300057
T. Padmanabhan
It is well known that the time dependent harmonic oscillator possesses a conserved quantity, usually called Ermakov-Lewis invariant. I provide a simple physical interpretation of this invariant as well as a whole family of related invariants. This interpretation does not seem to have been noticed in the literature before. The procedure also allows one to tackle some key conceptual issues which arise in the study of quantum fields in external, time dependent, backgrounds like in the case of particle production in an expanding universe and Schwinger effect.
众所周知,时变谐振子具有一个守恒量,通常称为Ermakov-Lewis不变量。我对这个不变量提供了一个简单的物理解释,以及一系列相关的不变量。这种解释在以前的文献中似乎没有被注意到。该过程还允许人们解决一些关键的概念问题,这些问题出现在外部,时间相关的背景下的量子场的研究中,比如在膨胀的宇宙中的粒子产生和施温格效应的情况下。
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引用次数: 22
Exponential or Power Law? How to Select a Stable Distribution of Probability in a Physical System 指数定律还是幂定律?如何在物理系统中选择一个稳定的概率分布
Pub Date : 2017-11-20 DOI: 10.3390/ecea-4-05009
A. D. Vita
A mapping of non-extensive statistical mechanics with non-additivity parameter q ≠ 1 into Gibbs’ statistical mechanics exists (E. Vives, A. Planes, PRL 88 2, 020601 (2002)) which allows generalization to q ≠ 1 both of Einstein’s formula for fluctuations and of the ’general evolution criterion’ (P. Glansdorff, I. Prigogine, Physica 30 351 (1964)), an inequality involving the time derivatives of thermodynamical quantities. Unified thermodynamic description of relaxation to stable states with either Boltzmann ( q = 1 ) or power-law ( q ≠ 1 ) distribution of probabilities of microstates follows. If a 1D (possibly nonlinear) Fokker-Planck equation describes relaxation, then generalized Einstein’s formula predicts whether the relaxed state exhibits a Boltzmann or a power law distribution function. If this Fokker-Planck equation is associated to the stochastic differential equation obtained in the continuous limit from a 1D, autonomous, discrete, noise-affected map, then we may ascertain if a a relaxed state follows a power-law statistics—and with which exponent—by looking at both map dynamics and noise level, without assumptions concerning the (additive or multiplicative) nature of the noise and without numerical computation of the orbits. Results agree with the simulations (J. R. Sanchez, R. Lopez-Ruiz, EPJ 143.1 (2007): 241–243) of relaxation leading to a Pareto-like distribution function.
存在一个非可加性参数q≠1的非扩展统计力学映射到Gibbs统计力学(E. Vives, A. Planes, PRL 88 2, 020601(2002)),它允许将爱因斯坦涨落公式和“一般演化准则”(P. Glansdorff, I. Prigogine, Physica 30 351(1964))推广到q≠1,这是一个涉及热力学量的时间导数的不等式。用玻尔兹曼(q = 1)或幂律(q≠1)分布的微观状态概率,给出松弛到稳定状态的统一热力学描述。如果一个一维(可能是非线性的)福克-普朗克方程描述了松弛状态,那么广义爱因斯坦公式预测了松弛状态是呈现玻尔兹曼分布函数还是幂律分布函数。如果这个福克-普朗克方程与在一维、自治、离散、受噪声影响的映射的连续极限中得到的随机微分方程相关联,那么我们就可以通过观察映射动力学和噪声水平来确定松弛状态是否遵循幂律统计——以及使用哪个指数,而不需要假设噪声的(加性或乘法性)性质,也不需要对轨道进行数值计算。结果与模拟结果一致(J. R. Sanchez, R. Lopez-Ruiz, EPJ 143.1(2007): 241-243),松弛导致Pareto-like分布函数。
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引用次数: 1
A Novel Asymptotic Solution to the Sommerfeld Radiation Problem: Analytic field expressions and the emergence of the Surface Waves Sommerfeld辐射问题的一种新的渐近解:解析场表达式和表面波的出现
Pub Date : 2017-10-06 DOI: 10.2528/PIERM17082806
S. Sautbekov, Sotiris Bourgiotis, A. Chrysostomou, P. Frangos
The well-known "Sommerfeld radiation problem" of a small -Hertzian- vertical dipole above flat lossy ground is reconsidered. The problem is examined in the spectral domain, through which it is proved to yield relatively simple integral expressions for the received Electromagnetic (EM) field. Then, using the Saddle Point method, novel analytical expressions for the scattered EM field are obtained, including sliding observation angles. As a result, a closed form solution for the subject matter is provided. Also, the necessary conditions for the emergence of the so-called Surface Wave are discussed as well. A complete mathematical formulation is presented, with detailed derivations where necessary.
重新考虑了平坦有损地面上小赫兹垂直偶极子的著名“索默菲尔德辐射问题”。本文在谱域对该问题进行了研究,通过谱域证明了该问题可以得到相对简单的接收电磁场积分表达式。然后,利用鞍点法,得到了包含滑动观测角度的散射电磁场解析表达式。因此,为主题提供了封闭形式的解决方案。并讨论了表面波产生的必要条件。给出了一个完整的数学公式,必要时还作了详细的推导。
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引用次数: 4
期刊
arXiv: Classical Physics
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