Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userPolarization singularities and M{o}bius strips in sound and water-surface waves
213
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We show that polarization singularities, generic for any complex vector field but so far mostly studied for electromagnetic fields, appear naturally in inhomogeneous yet monochromatic sound and water-surface (e.g., gravity or capillary) wave fields in fluids or gases. The vector properties of these waves are described by the velocity or displacement fields characterizing the local oscillatory motion of the medium particles. We consider a number of examples revealing C-points of purely circular polarization and polarization M{o}bius strips (formed by major axes of polarization ellipses) around the C-points in sound and gravity wave fields. Our results (i) offer a new readily accessible platform for studies of polarization singularities and topological features of complex vector wavefields and (ii) can play an important role in characterizing vector (e.g., dipole) wave-matter interactions in acoustics and fluid mechanics.
rate research
Read More
Spin is a fundamental yet somewhat enigmatic intrinsic angular-momentum property of quantum particles or fields, which appears within relativistic field theories. The spin density in wave fields is described by the theoretical Belinfante-Rosenfeld construction based on the difference between the canonical and kinetic energy-momentum tensors. These quantities have an abstract mathematical character and are usually considered as non-observable per se. Here we demonstrate, both theoretically and experimentally, that the Belinfante-Rosenfeld construction naturally arises in purely classical gravity (water surface) waves. There, the canonical momentum is associated with the generalized Stokes-drift phenomenon, while the spin is generated by subwavelength circular motion of water particles in inhomogeneous wave fields. Thus, we reveal the canonical spin and momentum in water waves and directly observe these fundamental relativistic field-theory properties as microscopic mechanical properties of particles in a classical wave system. Our findings shed light onto the nature of spin and momentum in wave fields, demonstrate the universality of field-theory concepts, and offer a new platform for studies of previously hidden aspects of quantum-relativistic physics.
A recent Letter has reported that sound waves can carry gravitational mass. I analyze this effect in a Hookes law solid, considering a wave packet moving in the $z$ direction with an amplitude that is independent of $x$ and $y$. The analysis shows that, at second order in an expansion around small amplitude vibrations, there is a small net motion of material, and thus mass, in the direction opposite to the wave packet propagation. This is a straightforward consequence of Newtons laws.
In the realm of Boltzmann-Gibbs (BG) statistical mechanics and its q-generalisation for complex systems, we analyse observed sequences of q-triplets, or q-doublets if one of them is the unity, in terms of cycles of successive Mobius transforms of the line preserving unity ( q=1 corresponds to the BG theory). Such transforms have the form q --> (aq + 1-a)/[(1+a)q -a], where a is a real number; the particular cases a=-1 and a=0 yield respectively q --> (2-q) and q --> 1/q, currently known as additive and multiplicative dualities. This approach seemingly enables the organisation of various complex phenomena into different classes, named N-complete or incomplete. The classification that we propose here hopefully constitutes a useful guideline in the search, for non-BG systems whenever well described through q-indices, of new possibly observable physical properties.
Typical flows in stellar interiors are much slower than the speed of sound. To follow the slow evolution of subsonic motions, various sound-proof equations are in wide use, particularly in stellar astrophysical fluid dynamics. These low-Mach number equations include the anelastic equations. Generally, these equations are valid in nearly adiabatically stratified regions like stellar convection zones, but may not be valid in the sub-adiabatic, stably stratified stellar radiative interiors. Understanding the coupling between the convection zone and the radiative interior is a problem of crucial interest and may have strong implications for solar and stellar dynamo theories as the interface between the two, called the tachocline in the Sun, plays a crucial role in many solar dynamo theories. Here we study the properties of gravity waves in stably-stratified atmospheres. In particular, we explore how gravity waves are handled in various sound-proof equations. We find that some anelastic treatments fail to conserve energy in stably-stratified atmospheres, instead conserving pseudo-energies that depend on the stratification, and we demonstrate this numerically. One anelastic equation set does conserve energy in all atmospheres and we provide recommendations for converting low-Mach number anelastic codes to this set of equations.
Microswimmers (planktonic microorganisms or artificial active particles) immersed in a fluid interact with the ambient flow, altering their trajectories. By modelling anisotropic microswimmers as spheroidal bodies with an intrinsic swimming velocity that supplements advection and reorientation by the flow, we investigate how shape and swimming affect the trajectories of microswimmers in surface gravity waves. The coupling between flow-induced reorientations and swimming introduces a shape dependency to the vertical transport. We show that each trajectory is bounded by critical planes in the position-orientation phase space that depend only on the shape. We also give explicit solutions to these trajectories and determine whether microswimmers that begin within the water column eventually hit the free surface. We find that it is possible for microswimmers to be initially swimming downwards, but to recover and head back to the surface. For microswimmers that are initially randomly oriented, the fraction that hit the free surface is a strong function of shape and starting depth, and a weak function of swimming speed.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
