# Physics - Classical Physics Publications (50)

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## Physics - Classical Physics Publications

We propose and experimentally achieve a directional dipole field radiated by an omnidirectional monopole source enclosed in a subwavelength structure of acoustically hybrid resonances. The whole structure in every dimension is an order smaller than the sound wavelength. The significance is that the radiation efficiency is up to 2. Read More

The aim of this work is to show that particle mechanics, both classical and quantum, Hamiltonian and Lagrangian, can be derived from few simple physical assumptions. Assuming deterministic and reversible time evolution will give us a dynamical system whose set of states forms a topological space and whose law of evolution is a self-homeomorphism. Assuming the system is infinitesimally reducible---specifying the state and the dynamics of the whole system is equivalent to giving the state and the dynamics of its infinitesimal parts---will give us a classical Hamiltonian system. Read More

We consider the relativistic generalization of the problem of the "least uncomfortable" linear trajectory from point A to point B. The traditional problem minimizes the time-integrated squared acceleration (termed the "discomfort"), and there is a universal solution for all distances and durations. This universality fails when the maximum speed of the trajectory becomes relativistic, and we consider the more general case of minimizing the squared proper acceleration over a proper time. Read More

In the present article the classical problem of electromagnetic scattering by a single homogeneous sphere is revisited. Main focus is the study of the scattering behavior as a function of the material contrast and the size parameters for all electric and magnetic resonances of a dielectric sphere. Specifically, the Pad\'e approximants are introduced and utilized as an alternative system expansion of the Mie coefficients. Read More

Manipulation of acoustic wavefronts by thin and planar devices, known as metasurfaces, has been extensively studied, in view of many important applications. Reflective and refractive metasurfaces are designed using the generalized reflection and Snell's laws, which tell that local phase shifts at the metasurface supply extra momentum to the wave, presumably allowing arbitrary control of reflected or transmitted waves. However, as it has been recently shown for the electromagnetic counterpart, conventional metasurfaces based on the generalized laws of reflection and refraction have important drawbacks in terms of power efficiency. Read More

The screened Coulomb interaction between a pair of infinite parallel planes with spatially varying surface charge is considered in the limit of small electrical potentials for arbitrary Debye lengths. A simple expression for the disjoining pressure is derived in terms of a two dimensional integral in Fourier space. The integral is evaluated for periodic and random charge distributions and the disjoining pressure is expressed as a sum over Fourier-Bloch reciprocal lattice vectors or in terms of an integral involving the autocorrelation function respectively. Read More

We provide an experimental framework where periodically driven PT-symmetric systems can be investigated. The set-up, consisting of two UHF oscillators coupled by a time-dependent capacitance, demonstrates a cascade of PT-symmetric broken domains bounded by exceptional point degeneracies. These domains are analyzed and understood using an equivalent Floquet frequency lattice with local PT-symmetry. Read More

Unusual electromagnetic disturbances resembling rings, loops, links, globules, lines, knots, roses and clouds are introduced, the generation of these disturbances in the laboratory is briefly considered and some possible directions for future research are highlighted. Read More

The most general linear and local set of boundary conditions, involving relations between the normal components of the D and B vectors and tangential components of the E and H vectors at each point of the boundary, are considered in this paper. Reflection of a plane wave from a boundary defined by general conditions in an isotropic half space is analyzed and an analytic expression for the reflection dyadic is derived. It is shown that any plane wave can be decomposed in two components which do not interact in reflection. Read More

We investigate the q-statistics of n harmonic oscillators appealing to the mathematical tools used in [EPJB 89, 150 (2016) and arXiv:1702.03535 (2017)] We obtain both bound and unbound states and also detect gravitational effects. Read More

After a short critique of the Minkowski formulae for the electromagnetic constitutive laws in moving media, we argue that in actual fact the problem of Lorentz-covariant electromagnetic response theory is automatically solved within the framework of modern microscopic electrodynamics of materials. As an illustration, we first rederive the well-known relativistic transformation behavior of the microscopic conductivity tensor. Thereafter, we deduce from first principles the long-sought-after transformation law of the wavevector- and frequency-dependent dielectric tensor under Lorentz boost transformations. Read More

A general method of description of a spontaneously polarized isotropic dielectric is constructed. It is based on the Maxwell equations for a medium and on the statistical averaging of the sources of spontaneous polarization (dipoles or multipoles). We show that the sources of spontaneous polarization in the Maxwell equations should be considered as conditionally foreign charges. Read More

In this work a design is proposed for an active, permanent magnet based, self-propelled magnetic bearing i.e. levitating motor having the following features : (a) simple winding structure, (b) high load supporting capacity, (c) no eccentricity sensors, (d) stable confinement in all translational dimensions, (e) stable confinement in all rotational dimensions and (f) high efficiency. Read More

Surface scattering of neutral helium beams created by supersonic expansion is an established technique for measuring structural and dynamical properties of surfaces on the atomic scale. Helium beams have also been used in Fraunhofer and Fresnel diffraction experiments. Due to the short wavelength of the atom beams of typically 0. Read More

**Affiliations:**

^{1}JAD,

^{2}LAMA

This paper describes an efficient algorithm for computing steady two-dimensional surface gravity wave in irrotational motion. The algorithm complexity is O(N log N), N being the number of Fourier modes. The algorithm allows the arbitrary precision computation of waves in arbitrary depth, i. Read More

The paradox of a free falling radiating charged particle in a gravitational field, is a well-known fascinating conceptual challenge that involves classical electrodynamics and general relativity. We discuss this paradox considering the emission of radiation as a consequence of an explicit space/time symmetry breaking involving the electric field within the trajectory of the particle seen from an external observer. This occurs in certain particular cases when the relative motion of the charged particle does not follow a geodesic of the motion dictated by the explicit Lagrangian formulation of the problem and thus from the metric of spacetime. Read More

Our experiment shows that the thermal emission of phonon can be controlled by magnetic resonance (MR) mode in a metasurface (MTS). Through changing the structural parameter of metasurface, the MR wavelength can be tuned to the phonon resonance wavelength. This introduces a strong coupling between phonon and MR, which results in an anticrossing phonon-plasmons mode. Read More

This paper revisits the interesting case of bounds on the Q-factor for a given directivity for small antennas. A higher directivity in a small antenna is closely connected with a narrow impedance bandwidth. The relation between bandwidth and a desired directivity is still not fully understood, not even for small antennas. Read More

Waves can be used to probe and image an unknown medium. Passive imaging uses ambient noise sources to illuminate the medium. This paper considers passive imaging with moving sensors. Read More

An invertible field transformation is such that the old field variables correspond one-to-one to the new variables. As such, one may think that two systems that are related by an invertible transformation are physically equivalent. However, if the transformation depends on field derivatives, the equivalence between the two systems is nontrivial due to the appearance of higher derivative terms in the equations of motion. Read More

Some modal (or decoupled) transmission-line properties such as per-unit-length impedance, admittance, or characteristic impedance have long been held to be, in general, non-unique. This ambiguity arises from the nature of the similarity transformations used to relate the terminal and modal domains, for which the voltage transformation matrix has been shown to be only loosely related to the corresponding current transformation matrix. Modern methods have attempted to relate the two, but these relations typically rely on arbitrary normalizations, leading to strictly incorrect and/or non-unique results. Read More

We present a procedure for the systematic estimation of the dispersion properties of linear discrete systems with periodic time-varying coefficients. The approach relies on the analysis of a single unit cell, making use of Bloch theorem along with the application of a harmonic balance methodology over an imposed solution ansatz. The solution of the resulting eigenvalue problem is followed by a procedure that selects the eigen-solutions corresponding to the ansatz, which is a plane wave defined by a frequency-wavenumber pair. Read More

This paper investigates the behavior of a heavy soft spring in steady circular motion. Since the spring is inhomogeneous due to centrifugal force, one can rigorously prove that it follows the one-dimensional quasi-static Willis equations instead of the Hooke's law. The theoretical predictions agree very well with experimental results. Read More

This article presents and discusses the general features and aspects regarding the electromagnetic scattering by a small core-shell sphere. First, the thickness effects on the plasmonic resonances are presented in the electrostatic (Rayleigh) limit, utilizing the MacLaurin expansion of the Mie coefficients of hollow scatterers. The results obtained are connected with the plasmon hybridization model, enhancing the applicability range of the electrostatic perspective. Read More

In this paper, we discuss the problem of determination of light radiation pressure force upon an anisotropic surface. The anisotropy of optical parameters is considered to have major and minor axes so the model is called as an orthotropic model. We derive the equations for the force components from the emission, absorption, and reflection, utilizing the modified Maxwell specular-diffuse model. Read More

Existing designs of transformation acoustic cloaks are not easy to implement in many practical situations because of their large dimensions, while scattering cancellation cloaks do not protect the inner cloak volume. Here we report implementation of an acoustic metamaterial exhibiting cylindrical dispersion in an ultra-thin (~1mm) and ultra-lightweight (~3g) acoustic cloak design intended to protect a human-head-size object in air, which combines scattering cancellation in the far-field with efficient sound proofing of the inner cloak volume. Read More

The principle of material frame indifference is shown to be incompatible with the basic balance laws of continuum mechanics. In its role of providing constraints on possible constitutive prescriptions it must be replaced by the classical principle of Galilean invariance. Read More

The ability to control electromagnetic fields, heat currents, electric currents, and other physical phenomena by coordinate transformation methods has resulted in novel functionalities, such as cloaking, field rotations, and concentration effects. Transformation optics, as the underlying mathematical tool, has proven to be a versatile approach to achieve such unusual outcomes relying on materials with highly anisotropic and inhomogeneous properties. Most applications and designs thus far have been limited to functionalities within a single physical domain. Read More

The dynamics of a passive scalar gradient experiencing fluctuating velocity gradient through the Lagrangian variations of strain persistence is studied. To this end, a systematic, numerical analysis based on the equation for the orientation of the gradient of a non-diffusive scalar in two-dimensional flow is performed. When the gradient responds weakly its orientation properties are determined by the mean value of strain persistence. Read More

A one-dimensional (1D) $q$-state Potts model with $N$ sites, $m$-site interaction $K$ in a field $H$ is studied for arbitrary values of $m$. Exact results for the partition function and the two-point correlation function are obtained at $H=0$. The system in a field is shown to be self-dual. Read More

Schroeder diffuser is a classical design, proposed over 40 years ago, for artificially creating optimal and predictable sound diffuse reflection. It has been widely adopted in architectural acoustics and it has also shown substantial potential in noise control, ultrasound imaging, microparticle manipulation, among others. The conventional Schroeder diffuser, however, has a considerable thickness on the order of one wavelength, severely impeding its applications for low frequency sound. Read More

After more than a century of debate, there remains continuing discomfort over what is the correct expression for the electromagnetic momentum in a dielectric medium. This is the so-called the Minkowski-Abraham controversy. We show that there is indeed a consistent picture for the electromagnetic momentum associated with waves in a dielectric, but one must start with the fields E and B, not D and H as fundamental objects. Read More

Implementing the modal method in the electromagnetic grating diffraction problem delivered by the curvilinear coordinate transformation yields two important results at once: analytical confirmation of the Rayleigh hypothesis, and a general analytical solution to the 1D grating diffraction problem in a form of a T-matrix. Read More

A technique is proposed for simulation of space-time varying metasurface discontinuity, discontinuity of both electric and magnetic fields. The technique is based on modifying conventional Finite Difference Time Domain (FDTD) method where the effect of the discontinuity is taken into account by introducing virtual nodes around the discontinuity. The fields on the discontinuity is calculated by using Generalized Sheet Transition Conditions, GSTCs. Read More

We propose a simple method based on Aperture Antennas Theory to assess limitations of OAM antennas in far-field links. Additional insight is also given by analyzing the eigenvalue problem related to the operators defining the source and far-field distributions for a given order of the vortex. The outcomes fully agree with the results recently achieved by Edfors, Craeye, and co-authors, and emphasize some additional draw-back. Read More

Relativistic Coulomb systems are studied in velocity space, prompted by the fact that the study of Newtonian Kepler/Coulomb systems in velocity space provides a method much simpler (and more elegant) than the familiar analytic solutions in ordinary space. The key for the simplicity and elegance of the velocity-space method is the linearity of the velocity equation, which is a unique feature of $1/r$ interactions for Newtonian and relativistic systems alike, allowing relatively simple analytic discussion with coherent geometrical interpretations. Relativistic velocity space is a 3-D hyperboloid ($H^3$) embedded in a 3+1 pseudo-Euclidean space. Read More

We formulate the theory of shortcuts to adiabaticity in classical mechanics. For a reference Hamiltonian, the counterdiabatic term is constructed from the dispersionless Korteweg-de Vries (KdV) hierarchy. Then the adiabatic theorem holds exactly for an arbitrary choice of time-dependent parameters. Read More

We show theoretically and experimentally that the propagation of an acoustic wave in an airflow duct going through a pair of diaphragms, with equivalent amount of mean-flow-induced effective gain and loss, displays all the features of a parity-time (PT) symmetric system. Using a scattering matrix formalism, we observe experimentally the properties which reflect the PT-symmetry of the scattering acoustical system: the existence of a spontaneous symmetry breaking with symmetry-broken pairs of scattering eigenstates showing amplification and reduction, and the existence of points with unidirectional invisibility. Read More

We propose the concept of a bianisotropic metasurface with controllable angular scattering. We illustrate this concept with the synthesis and the analysis of a metasurface exhibiting controllable absorption and transmission phase as function of the incidence angle. Read More

The Dirac's method for constrained systems is applied to the analysis of time-dependent Hamiltonians in the extended phase space. Our analysis provides a conceptually complete description and offers a different point of view of earlier works. We show that the Lewis invariant is a Dirac's observable and in consequence, it is invariant under time-reparametrizations. Read More

A drop of water that freezes from the outside-in presents an intriguing problem: the expansion of water upon freezing is incompatible with the self-confinement by a rigid ice shell. Using high-speed imaging we show that this conundrum is resolved through an intermittent fracturing of the brittle ice shell and cavitation in the enclosed liquid, culminating in an explosion of the partially frozen droplet. We propose a basic model to elucidate the interplay between a steady build-up of stresses and their fast release. Read More

We use group theoretic ideas and coset space methods to deal with problems in polarization optics of a global nature. These include the possibility of a globally smooth phase convention for electric fields for all points on the Poincar\'{e} sphere, and a similar possibility of real or complex bases of transverse electric vectors for all possible propagation directions. It is shown that these methods help in understanding some known results in an effective manner, and in answering new questions as well. Read More

In this paper, we design, fabricate and experimentally characterize a broadband acoustic right-angle bend device in air. Perforated panels with various hole-sizes are used to construct the bend structure. Both the simulated and the experimental results verify that acoustic beam can be rotated effectively through the acoustic bend in a wide frequency range. Read More

The regularity of earthquakes, their destructive power, and the nuisance of ground vibration in urban environments, all motivate designs of defence structures to lessen the impact of seismic and ground vibration waves on buildings. Low frequency waves, in the range $1$ to $10$ Hz for earthquakes and up to a few tens of Hz for vibrations generated by human activities, cause a large amount of damage, or inconvenience, depending on the geological conditions they can travel considerable distances and may match the resonant fundamental frequency of buildings. The ultimate aim of any seismic metamaterial, or any other seismic shield, is to protect over this entire range of frequencies, the long wavelengths involved, and low frequency, have meant this has been unachievable to date. Read More

In this article we propose a new design methodology to control both amplitude and phase of electromagnetic waves from cylindrical incidence, which utilizes engineered media that does not resort to transformation optics or its quasi-conformal approximations. This method can lead to two-dimensional isotropic, inhomogeneous material profiles of permittivity and permeability, to which a general class of scattering-free wave solutions arise. Our design is based on the separation of the complex wave solution into amplitude and phase. Read More

**Affiliations:**

^{1}PUCPR,

^{2}PUCPR,

^{3}LAMA,

^{4}PUCPR

Implicit schemes have been extensively used in building physics to compute the solution of moisture diffusion problems in porous materials for improving stability conditions. Nevertheless, these schemes require important sub-iterations when treating non-linear problems. To overcome this disadvantage, this paper explores the use of improved explicit schemes, such as Dufort-Frankel, Crank-Nicolson and hyperbolisation approaches. Read More

Magnetic dipolar modes (MDMs) in a quasi 2D ferrite disk are microwave energy eigenstate oscillations with topologically distinct structures of rotating fields and unidirectional power flow circulations. At the first glance, this might seem to violate the law of conservation of an angular momentum, since the microwave structure with an embedded ferrite sample is mechanically fixed. However, an angular momentum is seen to be conserved if topological properties of electromagnetic fields in the entire microwave structure are taken into account. Read More

Workhorse theories throughout all of physics derive effective Hamiltonians to describe slow time evolution, even though low-frequency modes are actually coupled to high-frequency modes. Such effective Hamiltonians are accurate because of \textit{adiabatic decoupling}: the high-frequency modes `dress' the low-frequency modes, and renormalize their Hamiltonian, but they do not steadily inject energy into the low-frequency sector. Here, however, we identify a broad class of dynamical systems in which adiabatic decoupling fails to hold, and steady energy transfer across a large gap in natural frequency (`steady downconversion') instead becomes possible, through nonlinear resonances of a certain form. Read More

There are three kind of losses in transmission lines: ohmic, dielectric and radiation losses. While the first two are local phenomena which are easy to model, the radiation losses lack a simple model. This work analyzes the radiation losses from two conductors transmission lines in free space, and derives a radiation model within the RLGC transmission lines model. Read More

In the present work the authors revisit a classical problem of crack propagation in a lattice. Authors investigate the questions concerning possible admissible steady-state crack propagations in an anisotropic lattice. It was found that for certain values of contrast in elastic and strength properties of a lattice the stationary crack propagation is impossible. Read More