Search arXiv⌕ Search

SEARCH · Search arXiv

Results for “physics.class-ph”

Search indexed arXiv papers on artificial intelligence, large language models, computer vision and robotics. Read source abstracts and follow links to arXiv.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 73 records · Page 4Linked to original sources
arXiv2008

The Fundamentals of Generalized Electrodynamics

The article presents an alternative approach to the definition of vector electrodynamic potential and its properties. It is shown that generally it has vortical and potential components. The system of differential equations of generalized electrodynamics (the macroscopical theory) is written down; and on the basis of these equations the mechanism of occurrence of the electromagnetic waves spreading in the direction of vector (longitudinal E-waves) is explained. It is demonstrated that the new macroscopical theory is in accordance with quantum electrodynamics. The author investigates the issue of physical pithiness of longitudinal electromagnetic E-waves and specifies the references to the experimental researches confirming the new theory.

physics.gen-ph↗
arXiv2008

Stability Theory and the Foundations of Physics: A Challenge to Real Analysis and Numerical Calculation

At present, there exists no physically plausible example of a quantum field theory for which the existence of solutions has been proven mathematically. The Clay Mathematics Institute has offered a prize for proving existence for a class of Yang-Mills theories defined by Jaffe and Witten. This paper proposes a multi-stage strategy for proving existence for a quantum version of the "'tHooft Polyakov" (tP) field theory, and argues that this theory, while not renormalizable or physically plausible as it stands, opens up a clear path to a physically plausible well-defined theory. The key initial challenge is to first prove stability for a classical version of this theory, in the spirit of Walter Strauss. The stability results of Bogomolnyi for classical PDE systems are widely cited as a foundation of string theory, but they leave key questions unaddressed, and may even call for small modifications of the tP model itself. This paper calls attention to the questions which require more attention, and proposes some partial possible answers. It also specifies a new numerical method to check for stability for the usual "hedgehog" types of solution, a method which may have broader potential uses for any ODE problems where accuracy in derivatives is as important as accuracy in function values.

physics.gen-ph↗
arXiv2008

Cherenkov radiation has nothing to do with X-shaped Localized Waves (Comments on "Cherenkov-Vavilov Formulation of X-Waves")

The Localized Waves are nondiffracting ("soliton-like") and self-reconstructing solutions to the wave equations, and are known to exist with subluminal, luminal and superluminal peak-velocities. The most studied ones are the "X-shaped" superluminal waves; which are associated with a cone, so that some authors [e.g., Walker and Kuperman, PRL 99 (Dec.2007) 244802] have been tempted to link them with Cherenkov radiation. However, the "X-waves" belong to a different realm, and exist even in the vacuum, independently of any media, as verified in a number of papers [listed e.g. in "Localized Waves" (J.Wiley; Jan.2008)]. We want to clarify the whole question on the basis of rigorous formalism and clear physical considerations. In particular, by explicit calculations based on Maxwell equations only, we show that: (i) the X-waves exist also inside both the front and the rear part of their double cone (that has nothing to do with Cherenkov's); (ii) they are to be found not via ad hoc assumptions, but by use of strict mathematical (or experimental) procedures; (iii) the ideal X-waves possess infinite energy, but finite-energy X-waves can be easily constructed (even without space-time truncations): And we do construct exact finite-energy solutions (totally free from backward-traveling waves); (iv) an actual attempt at comparing Cherenkov radiation with X-waves would lead one to consider the very different situation of the (X-shaped, too) field generated by a superluminal point-charge, a question exploited in previous papers [Recami et al., PRE 69 (2004) 027602]: We show explicitly, here, that the point-charge would not lose energy in the vacuum, and its field would not need to be continuously feeded by incoming side-waves (as it is the case, indeed, for an ideal, ordinary X-wave).

physics.optics↗
arXiv2009

The evolution of the phase space density of particle beams in external fields

The evolution of the phase space density of particle beams in external fields is found proceeding from the continuity equation in the six-dimensional (6D) phase space (mu-space). The Robinson theorem, which includes the Liouville theorem as a special case, was proved in a more simple and consistent alternative way valid for arbitrary external fields, averaged fields of the beam (self-generated electro-magnetic fields except intrabeam scattering) and arbitrary frictional forces (linear, nonlinear). It includes particle accelerators as a special case. The limits of the applicability of the Robinson theorem in case of cooling of excited ions having a finite living time are presented.

physics.class-ph↗
arXiv2008

Thump, ring: the sound of a bouncing ball

A basketball bounced on a stiff surface produces a characteristic loud thump, followed by high-pitched ringing. Describing the ball as an inextensible but flexible membrane containing compressed air, I formulate an approximate theory of the generation of these sounds and predict their amplitudes and waveforms.

physics.pop-ph↗
arXiv2009

A sphere moving down the surface of a static sphere and a simple phase diagram

A small sphere placed on the top of a big static frictionless sphere, slips until it leaves the surface at an angle $θ_{l}=\cos^{-1}{2/3}$. On the other extreme, if the surface of the big sphere has coefficient of static friction, $μ_s\to\infty$, the small sphere starts rolling and continues to do so until it leaves the surface at an angle $θ_{l} =\cos^{-1}{10/17}$. In the case where, $0\leqμ_s<\infty$, we get a simple phase diagram. The three phases are pure rolling, rolling with slipping and detached state. One phase line separates pure rolling from rolling with slipping. This diagram is obtained when stopping angles for pure rolling are plotted against static friction coefficients $μ_s$. Study in this article is restricted to the case when the mobile sphere starts at the top of the static sphere with infinitesimal kinetic energy.

physics.class-ph↗
arXiv2008

Relative-Velocity-Dependent Weber-type Models in Electromagnetism

This article reconsiders the relative-velocity-dependent approach to modeling electromagnetism that was proposed initially by Weber before data from cathode-ray-tube (CRT) experiments was available. It is shown that identifying the nonlinear, relative-velocity terms using CRT data results in a model, which not only captures standard relativistic effects in optics, high-energy particles, and gravitation, but also explains apparent discrepancies between predicted and measured energy (i) in high-energy-particle absorption experiments and (ii) in the classical beta-ray spectrum of radium-E.

physics.gen-ph↗
arXiv2008

Experimental Validation of Simplified Free Jet Turbulence Models Applied to the Vocal Tract

Sound production due to turbulence is widely shown to be an important phenomenon involved in a.o. fricatives, singing, whispering and speech pathologies. In spite of its relevance turbulent flow is not considered in classical physical speech production models mostly dealing with voiced sound production. The current study presents preliminary results of an experimental validation of simplified turbulence models in order to estimate the time-mean velocity distribution in a free jet downstream of a tube outlet. Aiming a future application in speech production the influence of typical vocal tract shape parameters on the velocity distribution is experimentally and theoretically explored: the tube shape, length and the degree and geometry of the constriction. Simplified theoretical predictions are obtained by applying similarity solutions of the bidimensional boundary layer theory to a plane and circular free jet in still air. The orifice velocity and shape are the main model input quantities. Results are discussed with respect to the upper airways and human sound production.

physics.class-ph↗
arXiv2012

Measuring the internal clock of the electron

The existence of an internal frequency associated to any elementary particle conjectured by de Broglie is compared with a classical description of the electron, where this internal structure corresponds to the motion of the centre of charge around the centre of mass of the particle. This internal motion has a frequency twice de Broglie's frequency, which corresponds to the frequency found by Dirac when analysing the electron structure. To get evidence of this internal electron clock a kind of experiment as the one performed by Gouanére et al. \cite{Gouanere} will show a discrete set of momenta at which a resonant scattering effect, appears. The resonant momenta of the electron beam are given by $p_k=161.748/k$ MeV$/c$, $k=1,2,3,...$, where only, the corresponding to $k=2$, was within the range of Gouanére et al. experiment. The extension of the experiment to other values of $p_k$, would show the existence of this phenomenon.

physics.class-ph↗
arXiv2008

On Cosmic Rays Sources

Study of astrophysical objects with strong dipolar magnetic fields show that the spectrum of the accelerated charged particles leaving the sources has a power law form with exponent -2.5, where the exponent is calculated on purely geometrical bases and is independent on the particle species.

astro-ph↗
arXiv2008

Lawn tennis balls, Rolling friction experiment and Trouton viscosity

We took three lawn tennis balls arbitrarily. One was moderately old, one was old and another was new. Fabricating a conveyor belt set-up we have measured rolling friction coefficients, $μ_{r}$, of the three balls as a function of their angular velocities, $ω_{ball}$. In all the three cases, plotting the results and using linear fits, we have obtained relations of the form $μ_{r}= k_{rol} ω_{ball}$ and have deduced the proportionality constant $k_{rol}$. Moreover, core of a lawn tennis ball is made of vulcanised India-rubber. Using the known values of Young modulus and shear viscosity of vulcanised India-rubbers in the theoretical formula for $k_{rol}$, we estimate $k_{rol}$s for the cores made of vulcanised India-rubbers, assuming Trouton ratio as three. The experimental results for the balls and the semi-theoretical estimates for the cores, of $k_{rol}$, are of the same order of magnitudes.

physics.class-ph↗
arXiv2009

On Fick's first law and the equations of quasi-static motion governing the molecular diffusion

The problem of the molecular diffusion in a biphasic fluid mixture is studied here from the two complementary points of view of Continuum Mechanics - in a somewhat different manner from Truesdell in "Mechanical basis of diffusion" (J. Chem. Physics (U.S.), 37 (1962) 2336-2344) - and that of Thermodynamics. It is established that the force involved in the 'diffusive drag', i.e. in the inter-constituent viscous friction, is necessarily linked to the relative diffusion velocity of one constituent with respect to the other. We also end up with Fick's first law, which appears to be a sufficient condition for the dissipated power associated with the diffusive motions to be positive.

physics.class-ph↗
arXiv2010

Tradeoff between Efficiency and Melting for a High-Performance Electromagnetic Rail Gun

We estimate the temperature distribution in the rails of an electromagnetic rail gun (EMG) due to the confinement of the current in a narrow surface layer resulting from the skin effect. In order to obtain analytic results, we assume a simple geometry for the rails, an electromagnetic skin effect boundary edge that propagates with the accelerating armature, and a current carrying channel controlled by magnetic field diffusion into the rails. We compute the temperature distribution in the rails at the time that the armature leaves the rails. For the range of exit velocities, from 1500 m/s to 5000 m/s, we find the highest temperatures are near the gun breech. After a single gun firing, the temperature reaches the melting temperature of the metal rails in a layer of finite thickness near the surface of the rails, for rails made of copper or tantalum. We plot the thickness of the melt layer as a function of position along the rails. In all cases, the thickness of the melt layer increases with gun velocity, making damage to the gun rails more likely at higher velocity. We also calculate the efficiency of the EMG as a function of gun velocity and find that the efficiency increases with increasing velocity, but only if the length of the gun is sufficiently long. The thickness of the melted layer also decreases with increasing rail length. Therefore, there is a tradeoff: for rails of sufficient length, the gun efficiency increases with increasing velocity but the melted layer thickness in the rails also increases.

physics.class-ph↗
arXiv2008

On the homogenization of orthotropic elastic composites by the strong-property-fluctuation theory

The strong-property-fluctuation theory (SPFT) provides a general framework for estimating the constitutive parameters of a homogenized composite material (HCM). We developed the elastodynamic SPFT for orthotropic HCMs, in order to undertake numerical studies. A specific choice of two-point covariance function - which characterizes the distributional statistics of the generally ellipsoidal particles that constitute the component materials - was implemented. Representative numerical examples revealed that the lowest-order SPFT estimate of the HCM stiffness tensor is qualitatively similar to the estimate provided by the Mori-Tanaka mean-field formalism, but the differences between the two estimates vary as the orthotropic nature of the HCM is accentuated. The second-order SPFT provides a correction to the lowest-order estimate of the HCM stiffness tensor and density. The correction, indicating effective dissipation due to scattering loss, increases as the HCM becomes less orthotropic but decreases as the correlation length becomes smaller.

physics.class-ph↗
arXiv2009

Minimal Magnetic Energy Theorem

Thomson's theorem states that static charge distributions in conductors only exist at the conducting surfaces in an equipotential configuration, yielding a minimal electrostatic energy. In this work we present a proof for this theorem based on the variational principle. Furthermore, an analogue statement for magnetic systems is also introduced and proven: the stored magnetic field energy reaches the minimum value for superficial current distributions so that the magnetic vector potential points in the same direction as the surface current. This is the counterpart of Thomson's theorem for the magnetic field. The result agrees with the fact that currents in superconductors are confined near the surface and indicates that the distinction between superconductors and hypothetical perfect conductors is fictitious.

physics.class-ph↗